Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Dokumenttyp
Schlagworte
- Quantum yield (77)
- Fluorescence (75)
- Nano (62)
- Lifetime (55)
- Dye (48)
- Quality assurance (43)
- Photophysics (41)
- Sensor (38)
- Photoluminescence (37)
- NIR (34)
- Particle (34)
- Lanthanide (33)
- Nanoparticle (32)
- Nanomaterial (30)
- Method (27)
- Upconversion (26)
- Surface chemistry (22)
- Mechanism (20)
- Synthesis (19)
- SWIR (18)
- Upconversion nanoparticle (18)
- Reference material (17)
- Energy transfer (15)
- Quantum dot (15)
- Quantum dots (14)
- Integrating sphere spectroscopy (13)
- Luminescence (13)
- Brightness (12)
- Multiplexing (11)
- Optical spectroscopy (11)
- Quantification (11)
- Quantitative spectroscopy (11)
- Single particle (10)
- Imaging (9)
- Nanoparticles (9)
- Aggregation (8)
- Assay (8)
- Bead (8)
- Uncertainty (8)
- Electron microscopy (7)
- Flow cytometry (7)
- Ligand (7)
- Polymer (7)
- Semiconductor quantum dot (7)
- Size (7)
- AIS (6)
- Barcoding (6)
- Calibration (6)
- Coating (6)
- Crystal (6)
- Encoding (6)
- Excitation power density (6)
- Life sciences (6)
- Microscopy (6)
- Optical probe (6)
- Silica (6)
- Surface analysis (6)
- Surface group analysis (6)
- Application (5)
- Bioimaging (5)
- Cell (5)
- IR (5)
- Measurement uncertainty (5)
- Modeling (5)
- Nanocrystal (5)
- Rare earth nanoparticles (5)
- SAXS (5)
- Semiconductor (5)
- Signal enhancement (5)
- Single particle spectroscopy (5)
- Stability (5)
- Standard (5)
- Surface (5)
- Switch (5)
- Temperature (5)
- Absolute fluorometry (4)
- Aging (4)
- Electrochemistry (4)
- Environment (4)
- Fluorescence standard (4)
- Image segmentation (4)
- InP (4)
- Iron oxide nanoparticles (4)
- Optical assay (4)
- PDT (4)
- Probe (4)
- Reference materials (4)
- Spectroscopy (4)
- TEM (4)
- Traceability (4)
- pH (4)
- AIE (3)
- Active fibers (3)
- Advanced Materials (3)
- Aggregation-induced emission (3)
- Antibody (3)
- BODIPY (3)
- Certification (3)
- Cleavable probe (3)
- Cr(III) (3)
- Cytotoxicity (3)
- Enhancement (3)
- Extracellular vesicles (EV) (3)
- Flourescence (3)
- Fluoride (3)
- Gold nanocluster (3)
- ICP-OES (3)
- In vivo imaging (3)
- Indium phosphide (3)
- Interlaboratory comparison (3)
- Label (3)
- Limit of detection (3)
- Linearity (3)
- Method development (3)
- Modelling (3)
- NMR (3)
- Nano particle (3)
- Optical assays (3)
- Particle Synthesis (3)
- Polarity (3)
- Quantitative NMR (3)
- Ratiometric sensors (3)
- Reference data (3)
- Reference product (3)
- Reporter (3)
- Safe-by-Design (3)
- Sensitization (3)
- Sensors (3)
- Solid state emission (3)
- Surface group quantification (3)
- Upconversion nanoparticles (3)
- Upconverting nanoparticles (3)
- XPS (3)
- Yb(III) complex (3)
- pH probe (3)
- pH sensing (3)
- 150th anniversary (2)
- ABC (2)
- Absolute fluorescence (2)
- Absolute fluorescence quantum yield (2)
- Advanced nanomaterials (2)
- Aggregation induced emission (2)
- Amorphous silica particles (2)
- Analysis (2)
- Analytical sciences (2)
- Automated image analysis (2)
- Automatisation (2)
- BAM (2)
- Bead-based assay (2)
- Bundesanstalt für Materialforschung und -prüfung (2)
- Cancer (2)
- Carbon dot (2)
- Cathodoluminescence (2)
- Cell studies (2)
- Characterization (2)
- Collection (2)
- Comparison (2)
- Conjugate (2)
- Contrast agent (2)
- Convolutional neural networks (2)
- Copolymer (2)
- Core-shell nanoparticles (2)
- Deactivation pathways (2)
- EMPIR 18HLT01 MetVesII (2)
- Engineered Nanomaterials (2)
- Enhancement strategy (2)
- Excitation (2)
- Exciton diffusion (2)
- FLIM (2)
- FRET (2)
- Flow cytometry (FCM) (2)
- Fluorescence decay kinetics (2)
- Fluorescent particles (2)
- Funtional Groups (2)
- Gold (2)
- Instrument calibration (2)
- Iron oxide (2)
- Jahrestag (2)
- Ligands (2)
- Llifetime (2)
- Magic-sized cluster (2)
- Mass spectrometry (2)
- Material sciences (2)
- Metal cluster (2)
- Method comparison (2)
- Method validation (2)
- Microparticle (2)
- Monitoring (2)
- Monomer (2)
- NIR-II (2)
- Nano- and microsensors (2)
- Nanomaterialien (2)
- Nanosafety (2)
- Nanosensor (2)
- Nanotoxicity (2)
- Neural networks (2)
- Optical Spectroscopy (2)
- Particle size (2)
- Particle surface analysis (2)
- Particle synthesis (2)
- Performance validation (2)
- Perovskite (2)
- Phosphor (2)
- Photoluminescence quantum yield (2)
- Photonic crystal (2)
- Pollutant (2)
- Polymer particle (2)
- Power density (2)
- Protein (2)
- Quantitative Analysis (2)
- Quantum Yield (2)
- Quantum yields (2)
- Quenching (2)
- Reliability (2)
- Safety (2)
- Semiconductor nanocrystal (2)
- Semiconductor nanocrystals (2)
- Sensing (2)
- Sensor molecules (2)
- Shape (2)
- Shell (2)
- Silica and Polystyrene Particles (2)
- Silica and polystyrene nanoparticles (2)
- Simulation (2)
- Singlet oxygen (2)
- Special issue (2)
- Standardization (2)
- Surface Group Analysis (2)
- Sythesis (2)
- Ternary quantum dots (2)
- Titration (2)
- Triplet-triplet annihilation (2)
- Upconversion nanocrystal (2)
- ZnSe (2)
- fluorescence (2)
- 18HLT01 MetVes II (1)
- 2D materials (1)
- A4F (1)
- AIS QD (1)
- ASAXS (1)
- Ab initio calculation (1)
- Absolute (1)
- Absolute measurement (1)
- Absorption (1)
- Advanced material (1)
- Advanced materials (1)
- Ag2S (1)
- Amplification (1)
- Analytical services (1)
- Antibody conjuagtes (1)
- Antibody conjugates (1)
- Aqueous quantum dot (1)
- Artificial Intelligence (1)
- Artificial intelligence (1)
- Artificial weathering (1)
- Au nanodisks (1)
- Au nanoparticles (1)
- Automated Image Analysis (1)
- Automated assay (1)
- Automated synthesis (1)
- Automation (1)
- Aza-BODIPY (1)
- Bacteria (1)
- Bacterial lipopolysaccharides (1)
- Bioconjugate (1)
- Biofilm (1)
- Biomimicry (1)
- Biosensing (1)
- Boron Neutron Capture Therapy (BNCT) (1)
- Brownsche Molekularbewegung (1)
- Bundesoberbehörden (1)
- C-dot (1)
- COSMO (1)
- CRP (1)
- CUINS2 nanocrystals (1)
- Calibrated fluorescence measurements (1)
- Capillary electrophoresis (1)
- Carboxyl group (1)
- Catalogue of services (1)
- Catch and release assay (1)
- Cement (1)
- Cement hydration (1)
- Certified reference material (1)
- Charge transfer (1)
- Chromium (III) complexes (1)
- Cleavable linker (1)
- Cleavable probes (1)
- Cluster (1)
- Colloidal semiconductor nanocrystals (1)
- Color (1)
- Color tuning (1)
- Complex (1)
- Conductometry (1)
- Conductor-like screening model (1)
- Converter marterial (1)
- Converter material (1)
- Core shell structure (1)
- Core/shell materials (1)
- Core/shell particle (1)
- Core/shell quantum dot (1)
- Corrosion (1)
- Cr(III) complex (1)
- Crosslinking (1)
- Cubical shape (1)
- Cyanine (1)
- DNA (1)
- DNA origami (1)
- DPA (1)
- Decay kinetics (1)
- Defect photoluminescence (1)
- Degradation (1)
- Design of experiment (1)
- Dipole moment (1)
- Dodecanethiol (1)
- Doping (1)
- Dual sensing (1)
- Dyad molecules (1)
- Dye labeling (1)
- Dyes (1)
- EC4SafeNano (1)
- EMPIR project (1)
- Editorial (1)
- Electrochemical Titration (1)
- Electrochemical titration (1)
- Electron Microscopy (1)
- Emission enhancement (1)
- Engineered nanomaterials (1)
- Er(III) (1)
- European Centre (1)
- Extracellualr vesicles (1)
- FTIR (1)
- Field sensor (1)
- Fluoranthene (1)
- Fluorescence intensity ratio (1)
- Fluorescence lifetime (1)
- Fluorescence microscopy (1)
- Fluorescence quantum yield (1)
- Fluorescence spectroscopy (1)
- Fluorescent dye (1)
- Fluorescent glasses (1)
- Fluorescent indicator (1)
- Fluorescent label (1)
- Fluorescent probe (1)
- Fluorophore (1)
- Forschungsstrategie (1)
- Fully aromatic frameworks (1)
- Functional group analysis (1)
- Functional group quantification (1)
- Functionalized Nanomaterials (1)
- Functionalized nano- and microparticles (1)
- Functionalized silica and polymeric particles (1)
- Gallium doping (1)
- Gold nanoclusters (1)
- Green synthesis (1)
- Heory (1)
- High-resolution transmission electron microscopy (1)
- Homogeneity (1)
- Hydration (1)
- IR spectroscopy; conductometry (1)
- Image Segmentation (1)
- Imaging techniques (1)
- Immunoassay (1)
- Infrastructure (1)
- Integrating sphere spectroscopy, (1)
- Interlaboratory (1)
- Interlabority comparison (1)
- K+ doped (1)
- LT-FCM (1)
- Lanthanide-doped nayf-4 (1)
- Lanthanides (1)
- Lead-free (1)
- Legionella (1)
- LiYF4 (1)
- Lichtstreuung (1)
- Lifetime analysis (1)
- Ligand exchange (1)
- Ligand quantification (1)
- Light harvesting (1)
- Luminescence lifetime measurments (1)
- Luorescence (1)
- MIC (1)
- MOF (1)
- MS (1)
- Magnetic (1)
- Medicine (1)
- Merocyanine (1)
- Metal (1)
- Metal-organic frameworks (1)
- Metasurface (1)
- Methos comparision (1)
- Microfluidics (1)
- Microorganism (1)
- Microparticles (1)
- Mie resonances (1)
- Moisture (1)
- Multicolored (1)
- Multifunctional efficiency (1)
- NIR dyes (1)
- NIR-II Imaging (1)
- NIR-II fluorescence (1)
- NIRII (1)
- Nanaoparticle (1)
- Nano CRM (1)
- Nano-safety (1)
- Nanocrystals (1)
- Nanomaterial design (1)
- Nanomaterials (1)
- Nanomedicine (1)
- Nanoparticle characterization (1)
- Nanopartikel (1)
- Nanoplatelet (1)
- Nanoplattform (1)
- Nanosafety (Safe-by-design) (1)
- Nanoscale luminescent reporters (1)
- Nanosensors (1)
- Nanotechnologie (1)
- Nd excitation (1)
- Near infrared (1)
- Near-infrared light (1)
- Neuartige Materialien (1)
- Neural Networks (1)
- Nicht lineare Prozesse (1)
- Nile Red (1)
- Nnano particle (1)
- Non lienear processes (1)
- Non-thermally coupled levels (1)
- One-pot synthesis (1)
- Optical Assays (1)
- Optical detection (1)
- Optical probes (1)
- Optical properties (1)
- Optical spectroscopie (1)
- Optical temperature sensing (1)
- Organic–inorganic nanostructures (1)
- Origami (1)
- Ovarian cancer (1)
- Oxygen (1)
- Oxygen sensing (1)
- Oxygen sensitive (1)
- PEG (1)
- PEG ligands (1)
- PH (1)
- PH probe (1)
- Particle architecture (1)
- Particle sensors (1)
- Particle, imaging (1)
- Partikelgrößenbestimmung (1)
- Partikelkonzentration (1)
- Passivation shell (1)
- Pd(II) (1)
- Perovskites (1)
- Ph (1)
- Phosphinine (1)
- Photocatalytic activity (1)
- Photon bunching (1)
- Photophysic (1)
- Photosensitizer (1)
- Photostability (1)
- Polymer particles (1)
- Polymers (1)
- Polystyrene microparticles (1)
- Polyurethane (1)
- Porosity (1)
- Porphyrin (1)
- Power density dependence (1)
- Pphotophysics (1)
- Production (1)
- Pseudomonas aeruginosa (1)
- Pt(II) (1)
- QNMR (1)
- Qantum yield (1)
- Quality assurcance (1)
- Quantenausbeute (1)
- Quantum Dot-Rod (1)
- Quantum Yields (1)
- Quantum chemistry (1)
- Quantum do (1)
- Quantum dot-rod (1)
- Quantum rod (1)
- Quinones (1)
- Ratiometric (1)
- Ratiometric Sensors (1)
- Ratiometric sensing (1)
- Redox (1)
- Reference methods (1)
- Reference nanomaterials (1)
- Reference nanoparticles (1)
- Reference particles (1)
- Reflection spectroscopy (1)
- Release (1)
- Reliable characterization (1)
- Renewable energy (1)
- Reproducibility (1)
- Reverse microemulsion (1)
- Risk assessment (1)
- Rreference material (1)
- SWIR photoluminescence (1)
- Saccharide sensing (1)
- Safer by design (1)
- Scattering (1)
- Self-assembly (1)
- Semiconductur (1)
- Shortwave infrared (1)
- Silanization (1)
- Silica Nanoparticles (1)
- Silica coating (1)
- Silica- and Polystyrene Particles (1)
- Silica- and polystyrene particles (1)
- Silicon nanoparticles (1)
- Silver indium sulfide (1)
- Single emitter (1)
- Single enhancement (1)
- Single molecule (1)
- Single-dot spectroscopy (1)
- Size and size distribution (1)
- Small angle x-ray scattering (1)
- Small-angle scattering (1)
- Solar cell (1)
- Solar cells (1)
- Solar concentrator (1)
- Solar energy (1)
- Solid (1)
- Spectroscopy / Instrumentation (1)
- Spectroscopy / Theory (1)
- SrF2 (1)
- Standardisierung (1)
- Standards (1)
- Stepwise growth (1)
- Surface Chemistry (1)
- Surface Modification (1)
- Surface coating (1)
- Surface functional group quantification (1)
- Surface group (1)
- Surface groups (1)
- Surface ligand (1)
- Surface modification (1)
- Surface modified nano- and microparticles (1)
- Sustainable-by-Design (1)
- Suzuki-Miyaura coupling (1)
- Swell-capture (1)
- TMDCs (1)
- Tag (1)
- Terminal functional groups (1)
- Theory (1)
- Theranostics (1)
- Therapy (1)
- Thermal coupling energy level (1)
- Thermally coupled levels (1)
- Thick shells (1)
- Thickness (1)
- Thiols (1)
- Time-gated emission (1)
- Time-resolved flow cytometry (1)
- Toxicity (1)
- Transition metal dichalcogenide (1)
- Transmission electron microscopy (1)
- Triggered (1)
- UV Vis (1)
- UpConversion (1)
- Upconverion (1)
- Upconversion luminescence (1)
- Upconverstion (1)
- VAMAS (1)
- X-ray (1)
- X-ray Photoelectron Spectroscopy (1)
- X-ray microspectroscopy (1)
- X-ray spectroscopy (1)
- aggregation-induced dual emission (AIDE) (1)
- anion-exchange (1)
- antibody (1)
- bacteria (1)
- bacteria detection (1)
- bioimaging (1)
- calibration (1)
- dye (1)
- flow cytometry (1)
- fluorescence microscopy (1)
- fluorescence standards (1)
- immunoseparation (1)
- lifetime (1)
- magnetic nanoparticle (1)
- method (1)
- nanoparticle (1)
- organic dyes (1)
- particle (1)
- photoluminescence (1)
- photophysics (1)
- quality assurcance (1)
- quantum dot (1)
- quantum yield (1)
- screening tes (1)
- surface group analysis (1)
- synthesis (1)
Organisationseinheit der BAM
- 1.2 Biophotonik (214) (entfernen)
Paper des Monats
- ja (7)
Eingeladener Vortrag
- nein (64)
Non-linear optical emitters are promising materials for energy applications and biotechnologies. Solid-state multi-band emitters like lanthanide doped up-conversion nanoparticles (UCNPs) show excellent photostability, are excitable in the near infrared (NIR), and show emission bands from the UV to SWIR spectral regions. The optical properties of these materials strongly depend on the excitation power density, i.e., the number of photons absorbed per time interval. The upconversion (ΦUC) and downshifting quantum efficiencies (ΦDS) of these materials, the excitation power dependent population, and the deactivation dynamics are influenced by nanoparticle architecture, doping concentration, and the microenvironment. We studied the fundamental changes of the luminescence properties of ß-NaYF4 UCNPs doped with Yb3+ and Er3+ depending on size, different surroundings such as aqueous and organic media, and different surface chemistries. We obtained further insights into shelling procedures, FRET optimization, influence of doping concentration, and advantages of different sensitizer ions.
The basics of absorption spectroscopy (termed also photometry) will be presented with focus on transparent solutions of different molecular and nanocrystalline absorbers and the ultraviolet (UV), visible (vis), and near-infrared (NIR) spectral region. Thereby, also typical sources of uncertainty will be addressed. Subsequently, several examples for typical applications of absorption measurements in the life and material sciences will be briefly shown ranging from aggregation studies and dye labeling densities of biomolecules (dye-to-biomolecule ratios) over optical assays for thiol and protein quantification to the optical determination of the size of semiconductor nanocrystals using size curves.
Semiconductor nanocrystals (quantum dots, QDs) are well known for their superior photophysical properties and enabled advancements in several key technologies of the 21st century and numerous technological applications. However, the most studied II-VI semiconductor nanocrystals contain the toxic heavy metal element cadmium, which is limiting their utilization in commercial applications. This has drawn the interest to alternative materials with less toxicity but having similar photophysical features.
The newest generation of TV screens based on QDs have shown that there is a promising environmentally friendly alternative with similar optoelectronic properties, namely indium phosphide (InP) QDs. InP QDs possess a bulk band gap of 1.35 eV with an exciton Bohr radius of ca. 10 nm and thus allow to tune their photoluminescence (PL) from the visible to the near-infrared. Tuning the size and shape of InP QDs and thus tailor their optoelectronic properties can be achieved by different strategies, which range from different types and concentrations of precursors, synthesis temperature or post-synthetic manipulations like etching. The incorporation of other elements like Gallium within the InP core synthesis is another possibility. Using a GaP intermediate layer before growing a ZnS shell has been shown to increase the PL quantum yield, which has been attributed to reduced lattice strain and the removal of phosphor vacancies. Different Ga precursors were investigated but a thorough investigation in terms of their reactivity, localization in the QD and influence on the photophysical properties is lacking to date.
In this contribution we will present the detailed investigation of the presence of two different Ga precursors within the InP core synthesis. Photophysical characterizations (steady-state and PL life-time measurements), transmission electron microscopy, XRD and EDX gave insights into the reactivity of the Ga precursors, the Ga localization in the InP core and influences on the photophysical properties. The variation of the precursor and surfactant concentration and the utilization of different ligands for the Ga precursor allowed tuning the PL emission towards the blue or the red. Depending on the used precursor type we observed the formation of larger-sized InP/GaP core/shell nanocrystals or the formation of InGaP alloy structures enabling to assess the blue range of emission (475 nm).
In summary, we report a highly modular solid TTA-UC system comprising of a crystalline, thermally stable PCN222(Pd) MOF with CA-coated MOF channels and with a DPA annihilator embedded in a solution-like environment in the MOF channels. This solid material displays blue upconverted delayed emission with a luminescence lifetime of 373 us, a threshold value of 329 mW*cm-2 and a triplet–triplet energy transfer efficiency of 82%. This optical application adds another facet to the versatile chemistry of PCN-222 MOFs. The design concept is also applicable to other TTA-UC pairs and enables tuning of the UCL color, for example, by replacing DPA with other dyes as exemplarily shown for 2,5,8,11-tetra-tert-butyl-perylene, that yields UCL at 450 nm. Current work aims to reduce the oxygen sensitivity and to increase the retention of the trapped annihilators in organic environments, for example, by tuning the chain length of the carboxylic acid and by coating the MOF surface. In addition, the TTA-UC efficiency will be further enhanced by reducing the reabsorption of the UC emission caused by Pd(TCPP) and by optimizing the sensitizer/annihilator interface.
In this contribution different ways are explored with the aim to generate suitable training data for ‘non-ideal’ samples using various approaches, e.g., computer-generated images or unsupervised learning algorithms such as generative adversarial networks (GANs). We used these data to train simple CNNs to produce segmentation masks of SEM images and tested the trained networks on real SEM images of complex nanoparticle samples. The novel use of CNN for the automated analysis of the size of nanoparticles of complex shape and with a high degree of agglomeration has proved to be a promising tool for the evaluation of particle size distribution on a large number of constituent particles. Further development and validation of the preliminary model, respectively larger training and validation data sets are necessary.
In this contribution different ways are explored with the aim to generate suitable training data for ‘non-ideal’ samples using various approaches, e.g., computer-generated images or unsupervised learning algorithms such as generative adversarial networks (GANs). We used these data to train simple CNNs to produce segmentation masks of SEM images and tested the trained networks on real SEM images of complex nanoparticle samples. The novel use of CNN for the automated analysis of the size of nanoparticles of complex shape and with a high degree of agglomeration has proved to be a promising tool for the evaluation of particle size distribution on a large number of constituent particles. Further development and validation of the preliminary model, respectively larger training and validation data sets are necessary.
Current trends in materials and life sciences are flanked by the need to push detection limits to single molecules or single cells, enable the characterization of increasingly complex matrices or sophisticated nanostructures, speed up the time of analysis, reduce instrument complexity and costs, and improve the reliability of data. This requires suitable analytical tools such as spectroscopic, separation and imaging techniques, mass spectrometry, and hyphenated techniques as well as sensors and their adaptation to application-specific challenges in the environmental, food, consumer product, health sector, nanotechnology, and bioanalysis. Increasing concerns about health threatening known or emerging pollutants in drinking water, consumer products, and food and about the safety of nanomaterials led to a new awareness of the importance of analytical sciences. Another important driver in this direction is the increasing demand by legislation, particularly in view of the 17 sustainable development goals by the United Nations addressing clean energy, industry, and innovation, sustainable cities, clean water, and responsible consumption and production. In this respect, also the development of analytical methods that enable the characterization of material flows in production processes and support recycling concepts of precious raw materials becomes more and more relevant. In the future, this will provide the basis for greener production in the chemical industry utilizing recycled or sustainable starting materials.
This makes analytical chemistry an essential player in terms of the circular economy helping to increase the sustainability of production processes. In the life sciences sector, products based on proteins, such as therapeutic and diagnostic antibodies, increase in importance. These increasingly biotechnologically produced functional biomolecules pose a high level of complexity of matrix and structural features that can be met only by highly advanced methods for separation, characterization, and detection. In addition, metrological traceability and target definition are still significant challenges for the future, particularly in the life sciences.
However, innovative reference materials as required for the health and food sector and the characterization of advanced materials can only be developed when suitable analytical protocols are available. The so-called reproducibility crisis in sciences underlines the importance of improved measures of quality control for all kinds of measurements and material characterization. This calls for thorough method validation concepts, suitable reference materials, and regular interlaboratory comparisons of measurements as well as better training of scientists in analytical sciences.
The important contribution of analytical sciences to these developments is highlighted by a broad collection of research papers, trend articles, and critical reviews from these different application fields. Special emphasis is dedicated to often-overlooked quality assurance and reference materials.
We demonstrate the potential of time-resolved luminescence spectroscopy for the straightforward assessment and in situ monitoring of the stability of upconversion nanocrystals (UCNPs). Therefore, we prepared hexagonal NaYF4:Yb3+,Er3+ UCNPs with various coatings with a focus on phosphonate ligands of different valency, using different ligand exchange procedures, and studied their dissolution behaviour in phosphate-buffered saline (PBS) dispersions at 20 °C and 37 °C with various analytical methods. The amount of the released UCNPs constituting fluoride ions was quantified by potentiometry using a Fluoride ion-sensitive electrode and particle disintegration was confirmed by transmission electron microscopy studies of the differently aged UCNPs. In parallel, the luminescence features of the UCNPs were measured with special emphasis on the lifetime of the sensitizer emission to demonstrate its suitability as Screening parameter for UCNP stability and changes in particle composition. The excellent correlation between the changes in luminescence lifetime and fluoride concentration highlights the potential of our luminescence lifetime method for UCNP stability screening and thereby indirect monitoring of the release of potentially hazardous fluoride ions during uptake and dissolution in biological systems. Additionally, the developed in situ optical method was used to distinguish the dissolution dynamics of differently sized and differently coated UCNPs.
The fast and accurate detection of disease-related biomarkers and potentially harmful analytes in different matrices is one of the main challenges in the life sciences. In order to achieve high signal-to-background ratios with frequently used photoluminescence techniques, luminescent reporters are required that are either excitable in the first diagnostic window or reveal luminescence lifetimes exceeding that of autofluorescent matrix components. Here, we demonstrate a reporter concept relying on broad band emissive ternary quantum dots (QDs) with luminescence lifetimes of a few hundred nanoseconds utilized for prolongating the lifetimes of organic or inorganic emitters with lifetimes in the order of a very few 10 ns or less through fluorescence resonant energy transfer. Using spectrally resolved and time-resolved measurements of the system optical response we demonstrate the potential of lifetime multiplexing with such systems exemplarily for AgInS2/ZnS and CdSe/ZnS QDs.
The optical properties of these materials strongly depend on the excitation power density, i.e., the number of photons absorbed per time interval. The upconversion quantum efficiencies (ΦUC) of these materials, the excitation power dependent population i.e. the emission characteristics, and the deactivation dynamics are influenced by nanoparticle architecture, doping concentration, and the microenvironment. We will discuss how time resolved measurements can help to understand the fundamental photophysical mechanisms and discuss differences to other nanocrystals like quantum dots.
Optical Thermometry is popular among researchers because of its non-contact, high sensitivity, and fast measurement properties. In the present experiment, Er3+/Yb3+/K+ co-doped NaYF4 nanoparticles with different K+ concentrations were synthesized by solvothermal method, and the samples showed bright upconversion green emission under the excitation of a 980 nm laser. The powder X-ray diffractometer and transmission electron microscope were used to characterize the crystal structure and its surface morphology, respectively. The spectral characteristics of nanoparticles with K+ doping concentration from 10% to 30% (Molar ratio) were investigated by fluorescence spectroscopy, and it was observed that the fluorescence intensity reached the maximum at the K+ concentration of 20%, after which the intensity weakened when the K+ content continued to increase. According to the dependence between the luminescence intensity of the sample and the laser power density and fluorescence lifetime, the intrinsic mechanism was carefully investigated. Temperature-dependent spectra of the samples were recorded in the temperature range of 315–495 K, and the maximum values of absolute sensitivity (Sa) and relative sensitivity (Sr) were measured at 0.0041 K−1 (455 K) and 0.9220%K−1 (315 K). The experimental results show that K+/Er3+/Yb3+ triple-doped NaYF4 green fluorescent nanoparticles (GFNs) have good prospects for applications in display devices, temperature sensing, and other fields.
BAM is currently building up a platform of novel nanoRMs relying on iron oxide nanoparticles of different shape, size and surface chemistry. Iron oxide was chosen as a core material because of its relevance to the material and life sciences.
As a first candidate of this series, we present cubic iron oxide nanoparticles with a nominal edge length of 8 nm. These particles were synthesized by thermal decomposition of iron oleate in high boiling organic solvents adapting well-known literature procedures. After dilution to a concentration suitable for electron microscopy (TEM and SEM) as well as for small-angle X-ray scattering (SAXS) measurements, the candidate nanoRM was bottled and assessed for homogeneity and stability by both methods following the guidelines of ISO 17034 and ISO Guide 35.
The particle sizes obtained by both STEM-in-SEM and TEM are in excellent agreement with a minimum Feret of 8.3 nm ± 0.7 nm. The aspect ratio (AR) of the iron oxide cubes were extracted from the images as the ratio of minimum Feret to Feret resulting in an AR of 1.18 for TEM to 1.25 for SEM. Alternatively, a rectangular bounding box was fitted originating from the minimum Feret and the longest distance through the particle in perpendicular direction. This led to AR values of 1.05 for TEM and 1.12 for SEM, respectively. The results confirm the almost ideal cubic shape.
Colloidal semiconductor nanoparticles with a spherical core and an elongated shell form bright emitters with a high absorption cross section. They show great potential for a multitude of optoelectronic applications such as LEDs or photovoltaic cells and can be used as gain material or as markers for bio imaging. For most of these applications high fluorescence quantum yields are a figure of merit for the emitter quality. In this work we investigate how the ensemble quantum yield is affected by the properties of the individual particles. In particular, we prove the role of non-emitting particles as well as the role of blinking. Using a combination of AFM and spatially resolved photoluminescence spectroscopy we measured hundreds of individual CdSe/CdS dot/rod particles of different shell lengths exciting with two different excitation wavelengths for shell or core excitation, respectively.
Colloidal semiconductor nanoparticles with a spherical core and an elongated shell form bright emitters with a high absorption cross section. They show great potential for a multitude of opto-electronic applications such as LEDs or photovoltaic cells and can be used as gain material or as markers for bio imaging. For most of these applications high fluorescence quantum yields are a figure of merit for the emitter quality. Our previous work showed that the ensemble quantum yields depend strongly on the shell size and the excitation wavelength. In this work we investigate how the ensemble quantum yield is affected by the properties of the individual particles. In particular, we prove the role of non-emitting particles as well as the role of blinking. Using a combination of AFM and spatially resolved photoluminescence spectroscopy we measured hundreds of individual CdSe/CdS dot/rod particles of different shell lengths exciting with two different excitation wavelengths for shell or core excitation, respectively.
The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery.
We report on the temperature- and structural-dependent optical properties and photophysics of a set of boron dipyrromethene (BODIPY) dyes with different substitution patterns of their meso-aryl subunit. Single-crystal Xray diffraction analysis of the compounds enabled a classification of the dyes into a sterically hindered and a unhindered group. The steric hindrance refers to a blocked rotational motion of the aryl subunit around the bond connecting this moiety to the meso-position of the BODIPY core. The energy barriers related to this rotation were simulated by DFT calculations. As follows from the relatively low rotational barrier calculated to about 17 kcal/mol, a free rotation is only possible for sterically unhindered compounds. Rotational barriers of more than 40 kcal/mol determined for the sterically hindered compounds suggest an effective freezing of the rotational motion in These molecules. With the aid of temperature-dependent spectroscopic measurements, we could show that the ability to rotate directly affects the optical properties of our set of BODIPY dyes. This accounts for the strong temperature dependence of the fluorescence of the sterically unhindered compounds which show a drastic decrease in fluorescence quantum yield and a significant shortening in fluorescence lifetime upon heating. The optical properties of the sterically hindered compounds, however, are barely affected by temperature. Our results suggest a nonradiative deactivation of the first excited singlet state of the sterically unhindered compounds caused by a conical intersection of the potential energy surfaces of the Ground and first excited state which is accessible by rotation of the meso-subunit. This is in good agreement with previously reported deactivation mechanisms. In addition, our results suggest the presence of a second nonradiative depopulation pathway of the first excited singlet state which is particularly relevant for the sterically hindered compounds.
Recent progress has shown that using wavelengths between 1,000 and 2,000 nm, referred to as the shortwave-infrared or near-infrared (NIR)-II range, can enable high-resolution in vivo imaging at depths not possible with conventional optical wavelengths.
However, few bioconjugatable probes of the type that have proven invaluable for multiplexed imaging in the visible and NIR range are available for imaging these wavelengths. Using rational design, we have generated persulfonated indocyanine dyes with absorbance maxima at 872 and 1,072 nm through catechol-ring and aryl-ring fusion, respectively, onto the nonamethine scaffold. Multiplexed two-color and three-color in vivo imaging using monoclonal antibody and dextran conjugates in several tumor models illustrate the benefits of concurrent labeling of the tumor and healthy surrounding tissue and lymphatics.
These efforts are enabled by complementary advances in a custom-built NIR/shortwave-infrared imaging setup and software package for multicolor real-time imaging.
The influence of solvent polarity and surface ligand rigidification on the SWIR emission profile of gold nanoclusters with an anistropic surface was investigated. A strong enhancement of the SWIR emission band at 1200 nm was observed when measuring in different local environments: in solution, in polymer composites, and in solids. SWIR in vivo imaging of mice assisted by deep learning after intravenous administration of these gold nanoclusters provides high definition pseudo-3D views of vascular blood vessels.
Atomically precise gold nanoclusters are a fascinating class of nanomaterials that exhibit molecule-like properties and have outstanding photoluminescence (PL). Their ultrasmall size, molecular chemistry, and biocompatibility make them extremely appealing for selective biomolecule labeling in investigations of biological mechanisms at the cellular and anatomical levels. In this work, we report a simple route to incorporate a preformed Au25 nanocluster into a model bovine serum albumin (BSA) protein. A new approach combining small-angle X-ray scattering and molecular modeling provides a clear localization of a single Au25 within the protein to a cysteine residue on the gold nanocluster surface.
Attaching Au25 to BSA strikingly modifies the PL properties with enhancement and a redshift in the second near-infrared (NIR-II) window. This study paves the way to conrol the design of selective sensitive probes in biomolecules through a ligand-based strategy to enable the optical detection of biomolecules in a cellular environment by live imaging.
Tris(3,5-dimethylpyrazolyl)arsane (1) is introduced as a low-cost and convenient to handle arsenic precursor for the straight Forward synthesis of InAs Quantum dots (QDs). Transamination of 1 with the solvent oleylamine (OLAH) gives trioleylarsane (As(OLA)3) which in the presence of the reducing agents diisobutylaluminum hydride (DIBAL-H) or trioleylphosphane (P(OLA)3) yields InAs QDs via a typical hot injection approach. The size of the obtained InAs core QDs are tuned by varying the reaction time, the amount of the applied reducing agent, or even more effectively by changing the Indium and/or zinc halide precursors, InX3, and ZnX2 (Cl, Br, or I). Passivation of the resulting InAs particles with a
protective ZnS or ZnSe shell results in improved photoluminescence of the core/shell QDs covering a spectral range between 600 and 1150 nm.
At present, the field of research on nanostructures is actively developing, which is due to their unique physico-chemical properties compared to bulk materials. Many research activities are focused on obtaining nanocomposites, which combine various types of nanostructures with different properties and function. For example, the development of magneto-luminescent nanocomposites makes it possible to use their luminescence for optical imaging, and their magnetic properties for magnetic targeted delivery and as agents of hyperthermia and magnetic resonance imaging.
My master studies as part of the project Goszadanie 2019-1080 at ITMO were focused on the investigation of nanocomposites, consisting of semiconductor quantum dots (QDs) as luminescent component and superparamagnetic iron oxide nanoparticles (SPIONs) as magnetic one, in solution and during their incubation with HeLa cells. The spectrally resolved analysis of the QD photoluminescence (PL) kinetics of the free QDs and the QDs incorporated in these nanocomposites undergoing energy transfer processes allowed for (1) understanding the reasons for the quenching of QD luminescence in cells, (2) evaluating the average distance between the QDs and, based on this, concluding the degree of QD aggregation in cells, and (3) drawing conclusions about the QD-quencher composites integrity in cells. Overall, the analysis of the PL kinetics confirmed that QDs and SPIONs remain bound in the obtained nanocomposites during incubation with cells.
To ensure the successful advancement of nanomaterials in biomedicine and the transition from their laboratory preparation and studies to their use in different applications and in industry, it is crucial to develop reliable measurement methods and reference materials candidates for the characterization of functional nanomaterials and assessing the quality of the obtained nanostructures. My recently started project at BAM, which is part of the EU metrology project MeTrINo, will be devoted to this topic. There we will focus on the development of methodologies for the synthesis and characterization of iron oxide nanoparticles, already used in biomedicine, and multi-element lanthanide-based nanoparticles with attractive upconversion luminescence, as reference materials with high monodispersity and reproducibility. Also, these nanoparticles will be functionalized with organic dyes for optical imaging and, probably, the study of the energy transfer phenomena.
Outer membrane lipopolysaccharides (LPS) play a crucial role in determining attachment behavior and pathogenicity of bacteria. The aim of this study was to develop a simple procedure for anchoring bacterial lipopolysaccharides to polystyrene (PS) microparticles as a model system for in situ attachment studies. By using a swellcapture methodology, commercially available LPS of Pseudomonas aeruginosa (strain ATCC 27316 serotype 10.22) was anchored onto PS microparticles in a proof-of-concept study. A detailed chemical and morphological characterization has proven the success of LPS incorporation. It was shown that the coverage and structure of the LPS film was concentration dependent. The procedure can easily be adapted to LPS of other bacterial strains to generate a synthetic model toolkit for attachment studies.
SWIR luminescent nanomaterials – key chemical parameters for bright probes for in vivo bioimaging
(2024)
A current challenge for studying physio-pathological phenomena and diseaserelated processes in living organisms with non-invasive optical bioimaging is the development of bright optical reporters that enable deep tissue penetration, a high detection sensitivity, and a high spatial and temporal resolution. The focus of this project are nanomaterials, which absorb and emit in the shortwave infrared (SWIR) between ~900–2500 nm where scattering, absorption, and autofluorescence of the tissue are strongly reduced compared to the visible and NIR.
An emerging class of inorganic optical reporters are nearinfrared (NIR) excitable lanthanide-based upconversion nanoparticles (UCNPs) with multicolor emission and long luminescence lifetimes in the range of several hundred microseconds. For the design of chemical sensors and optical probes that reveal analyte-specific changes in their spectroscopic properties, these nanomaterials must be combined with sensitive indicator dyes that change their absorption and/or fluorescence properties selectively upon interaction with their target analyte, utilizing either resonance energy transfer (RET) processes or reabsorption-related inner filter effects. The rational development of UCNP-based nanoprobes for chemical sensing and imaging in a biological environment requires reliable methods for the Surface functionalization of UCNPs, the analysis and quantification of Surface groups, a high colloidal stability of UCNPs in aqueous media as well as the chemically stable attachment of the indicator molecules, and suitable instrumentation for the spectroscopic characterization of the energy-transfer systems and the derived nanosensors. These topics are highlighted in the following feature article, and examples of functionalized core−shell nanoprobes for the sensing of different biologically relevant analytes in aqueous environments will be presented. Special emphasis is placed on the intracellular sensing of pH.
Organic and inorganic micro- and nanoparticles are increasingly used as drug carriers, fluorescent sensors, and multimodal labels in the life and material sciences. Typically, these applications require further functionalization of the particles with, e.g., antifouling ligands, targeting bioligands, stimuli-responjsive caps, or sensor molecules. Besides serving as an anchor point for subsequent functionalization, the surface chemistry of these particles also fundamentally influences their interaction with the surrounding medium and can have a significant effect on colloidal stability, particle uptake, biodistribution, and particle toxicity in biological systems. Moreover, functional groups enable size control and tuning of the surface during the synthesis of particle systems.
For these reasons, a precise knowledge of the chemical nature, the total number of surface groups, and the number of groups on the particle surface that are accessible for further functionalization is highly important. In this contribution, we will will discuss the advantages and limitiations of different approaches to quantify the amount of commonly used surface functional groups such as amino,[1,2] carboxy,[1,2] and aldehyde groups.[3] Preferably, the quantification is carried out using sensitive and fast photometric or fluorometric assays, which can be read out with simple, inexpensive instrumentation and can be validated by complimentary analytic techniques such as ICP-OES and quantitative NMR.
The absorption and emission properties of organic dyes are generally tuned by altering the substitution pattern. However, tuning the fluorescence lifetimes over a range of several 10 ns while barely affecting the spectral features and maintaining a moderate fluorescence quantum yield is challenging. Such properties are required for lifetime multiplexing and barcoding applications. Here, we show how this can be achieved for the class of fluoranthene dyes, which have substitution-dependent lifetimes between 6 and 33 ns for single wavelength excitation and emission. We explore the substitution-dependent emissive properties in the crystalline solid state that would prevent applications.
Furthermore, by analyzing dye mixtures and embedding the dyes in carboxyfunctionalized 8 μm-sized polystyrene particles, the unprecedented potential of these dyes as labels and encoding fluorophores for time-resolved fluorescence detection techniques is demonstrated.
We present a comparative study of the spectroscopic properties of the donor–acceptor–donor substituted dyes triphenylamine-allylidenemalononitrile-julolidine (TMJ) and triphenylamine-allylidenemalononitriletriphenylamine (TMT), bearing one and two propeller-like triphenylamine donor moieties, in solvents of varying polarity and viscosity and in the aggregated and solid state. Our results reveal control of the aggregation-induced spectroscopic changes and the packing motifs of the dye molecules in the solid state by the chemical nature and structure of the second nitrogen-containing donor, i.e., a planar and a rigid julolidine or a twisted triphenyl group. Assuming that the TMT and TMJ aggregates show a comparable arrangement of the molecules to the respective crystals, these different molecular interactions in the solid state are responsible for aggregation induced emission (AIE) in the case of TMT and its absence for TMJ. Moreover, a versatile strategy for the fluorescence enhancement of only weakly emissive AIE dyes is shown, turning these dyes into bright nanoscale fluorescent reporters by using them as stains for preformed polymer particles.
Photoluminescence techniques are amongst the most widely used tools in the life sciences, with new and exciting applications in medical diagnostics and molecular imaging continuously emerging. Advantages include their comparative ease of use, unique sensitivity, non-invasive character, and potential for multiplexing, remote sensing, and miniaturization. General drawbacks are, however, signals, that contain unwanted wavelength- and polarization contributions from instrument-dependent effects, which are also time-dependent due to aging of instrument-components, and difficulties to measure absolute fluorescence intensities. Moreover, scattering systems require special measurement geometries and the interest in new optical reporters with emission > 1000 nm strategies for reliable measurements in the second diagnostic for the comparison of material performance and the rational design of new fluorophores with improved properties.
Here, we present strategies to versatile method-adaptable liquid and solid fluorescence standards for different fluorescence parameters. Examples are multi-emitter glasses, spectral fluorescence standards, and quantum yield standards for the UV/vis/NIR.
Engineered nanoparticles (NPs) with various chemical compositions and surface functionalities are routinely fabricated for industrial applications such as medical diagnostics, drug delivery, sensing, catalysis, energy conversion and storage, opto-electronics, and information storage which improve the quality of life and European prosperity. NP function, performance, interaction with biological species, and environmental fate are largely determined by their surface functionalities. Standardized repeatable surface characterization methods are therefore vital for quality control of NPs, and to meet increasing concerns regarding their safety. Therefore, industry, regulatory agencies, and policymakers need validated traceable measurement methods and reference materials. This calls for fit-for-purpose, validated, and standardized methods, and reference data and materials on the surface chemistry of engineered NPs. Here, we present a concept for the development of such standardized measurement protocols utilizing method cross-validation and interlaboratory comparisons (ILCs) with emphasis on both advanced measurement methods such as quantitative Nuclear Magnetic Resonance (qNMR), X-ray photoelectron spectroscopy (XPS) and secondary ion mass spectrometry (SIMS) and cost-efficient, non-surface specific methods like optical assays and electrochemical titration methods.
Standardisation of concentration measurements of extracellular vesicles for medical diagnoses
(2020)
Extracellular vesicles (EVs) are cell-derived particles in body fluids, which have excellent potential as next generation biomarkers for the early diagnosis of common diseases, such as cancer and thrombosis. This project aims to tap into the clinical potential of EVs by developing traceable measurements of number concentration, size distribution, refractive index (RI) and fluorescence intensity of cell-specific EVs in human blood and urine.
To realise our aims, we will develop synthetic reference materials with physical properties resembling EVs (WP1), instrumentation and procedures to standardise EV measurements in clinical laboratories (WP2), and ready-to-use biological test samples (WP3). These will then be evaluated in an inter-laboratory comparison study across a range (>20) of standard flow cytometers in clinical labs (WP4).
Die gemeinsame Forschungsstrategie der Bundesoberbehörden zur Nanotechnologie wurde 2016 veröffentlicht. Die darin enthaltenen Aufgaben wurden von den Bundesoberbehörden vielfältig bearbeitet. Diese Präsentation gibt einen Überblick über die Projekte, die von der BAM bis 2019 bearbeitet wurden/werden und sich in den Rahmen der Forschungsstrategie einordnen.
Stability, dissolution, and cytotoxicity of NaYF4‑upconversion nanoparticles with different coatings
(2022)
Upconversion nanoparticles (UCNPs) have attracted considerable attention owing to their unique photophysical properties. Their utilization in biomedical applications depends on the understanding of their transformations under physiological conditions and their potential toxicity. In this study, NaYF4: Yb,Er UCNPs, widely used for luminescence and photophysical studies, were modified with a set of four different coordinatively bound surface ligands, i.e., citrate, alendronate (AA), ethylendiamine tetra(methylene phosphonate) (EDTMP), and poly(maleic anhydride-alt-1-octadecene) (PMAO), as well as silica coatings with two different thicknesses. Subsequently, the aging-induced release of fluoride ions in water and cell culture media and their cytotoxic profile to human keratinocytes were assessed in parallel to the cytotoxic evaluation of the ligands, sodium fluoride and the lanthanide ions. The cytotoxicity studies of UCNPs with different surface modifications demonstrated the good biocompatibility of EDTMP-UCNPs and PMAO-UCNPs, which is in line with the low amount of fluoride ions released from these samples. An efficient prevention of UCNP dissolution and release of cytotoxic ions, as well as low cytotoxicity was also observed for UCNPs with a sufficiently thick silica shell. Overall, our results provide new insights into the
understanding of the contribution of surface chemistry to the stability, dissolution behavior, and cytotoxicity of UCNPs. Altogether, the results obtained are highly important for future applications of UCNPs in the life sciences and bioimaging studies.
The increasing interest in molecular and nanoscale emitters with photoluminescence > 800 nm and recently also > 1000 nm for bioanalysis, medical diagnostics, bioimaging, and safety Barcodes requires quantitative spectroscopic studies, which are, however still challenging in this long wavelength region. This is of special relevance for nanocrystalline emitters like semiconductor quantum dots and rods as well as lanthanide-based upconversion and downconversion nanocrystals, where surface states and the accessibility of emissive states by quenchers largely control accomplishable photoluminescence quantum yields and hence, signal sizes and detection sensitivities from the reporter side. Moreover, nonlinear emitters like lanthanide-based upconversion nanocrystals require also power density-dependent studies of their luminescence spectra, quantum yields, and decay kinetics. Here, we present suitable absolute methods and underline the impact of such measurements on a profound mechanistic understanding of the nonradiative deactivation pathways in semiconductor and upconversion nanocrystals of different chemical composition and particle architecture.
Multiplexed encoding schemes of nano- and micrometer sized particles with fluorescent dyes or quantum dots (QDs) and their optical detection, are of increasing interest for applications in the life sciences, for example in flow cytometry. Almost all strategies utilizing fluorescence focus on spectrally distinguishable emission bands or colors and different intensity levels as fluorescence codes. The fluorescence parameter lifetime has been, however, barely exploited. In this work the goal is to perform multiplexing with encoding fluorophores with different fluorescence lifetimes (LTs). In comparison to the spectral multiplexing strategies this has the advantage, that the different fluorescence LT codes can be measured with the excitation and emission wavelength, thus reducing instrument costs. Moreover, LTs should not depend on emitter concentration. Unlike organic dyes, the LTs of which are typically < 10 ns, the fluorescence LTs of ternary semiconductor QDs that represent a “green” alternative to conventional Cd-containing QDs are in the range of several hundred ns, independent of oxygen concentration, and can be tuned to a certain extent by chemical composition and surface chemistry. This present a time region that can be barely covered by other emitters that have either much shorter or longer lifetimes. In this project, different encoding strategies will be assessed and the encoded particles will be then used for fluorescence assays for the analysis of several targets in parallel. Therefor the encoded particles will be functionalized with different target-specific bioligands and read out with a specifically designed flow cytometer enabling time-resolved fluorescence detection. With this instrument, the particles will be discriminated by their fluorescence LTs In one detection channel while the analytes will be quantified by fluorescence labels in a second channel in the intensity domain.
Lanthanide-doped NaYF4 upconversion nano- and microcrystals were synthesized via a facile solvothermal approach. Thereby, the influence of volume ratios of ethylene glycol (EG)/H2O, molar ratios of NH4F/RE3+ (RE3+ represents the total amount of Y3+ and rare-earth dopant ions), Gd3+ ion contents, types of activator dopant ions, and different organic co-solvents on the crystal phase, size, and morphology of the resulting particles were studied systematically. A possible formation mechanism for the growth of crystals of different morphology is discussed. Our results show that the transition from the α- to the β-phase mainly depends on the volume ratio of EG/H2O and the molar ratio of NH4F/RE3+, while the morphology and size could be controlled by the type of organic co-solvent and Gd3+ dopant ions. Furthermore, the reaction time has to be long enough to convert α-NaYF4 into β-NaYF4 during the growth process to optimize the upconversion luminescence. The formation of larger β-NaYF4 crystals, which possess a higher upconversion luminescence than smaller particles, proceeds via intermediates of smaller crystals of cubic structure. In summary, our synthetic approach presents a facile route to tailor the size, Crystal phase, morphology, and luminescence features of upconversion
materials.
N-Benzyl aroyl-S,N-ketene acetals can be readily synthesized by condensation of aroyl chlorides and N-Benzyl 2-methyl benzothiazolium salts in good to excellent yields, yielding a library of 35 chromophores with bright solid-state emission and aggregation-induced emission characteristics.
Varying the substituent from electron-donating to electronwithdrawing enables the tuning of the solid-state emission Color from deep blue to red.
Many applications of nanomaterials in the life sciences require the controlled functionalization of these materials with ligands like polyethylene glycol (PEG) and/or biomolecules such as peptides, proteins, and DNA. This enables to tune their hydrophilicity and biocompatibility, minimize unspecific interactions, improve biofunction-nalization efficiencies, and enhance blood circulation times and is the ultimate prerequisite for their use as reporters in assays or the design of targeted optial probes for bioimaging.
At the core of these functionalization strategies are reliable and validated methods for surface group and ligand quantification that can be preferably performed with routine laboratory instrumentation, require only small amounts of substances, and are suitable for many different types of nanomaterials.
We present here versatile and simple concepts for the quantification of common functional groups, ligands, and biomolecules on different types of organic and inorganic nano-materials, using different types of optical reporters and method validation with the aid of multimodal reporters and mass balances.
Two sets of polystyrene nanoparticles (PSNPs) with comparable core sizes but different carboxyl group densities were made and separated using asymmetric flow field flow fractionation (AF4), capillary electrophoresis (CE), and the off-line hyphenation of both methods. Our results revealed the significant potential of two-dimensional off-line AF4-CE hyphenation to improve the separation and demonstrated for the first time, the applicability of CE to determine the functional group density of nanoparticles (NPs). Compared to the result acquired with conductometric titration, the result obtained with synthesized 100 nm sized PSNPs revealed only a slight deviation of 1.7%. Commercial 100 nm sized PSNPs yielded a deviation of 4.6 %. For 60 nm sized PSNPs, a larger deviation of 10.6 % between both methods was observed, which is attributed to the lower separation resolution.
Photon upconversion nanomaterials have a wide range of applications, including biosensing and deep-tissue imaging. Their typically very weak and narrow absorption bands together with their size dependent luminescence efficiency can limit their application potential. This has been addressed by increasingly sophisticated core-shell particle architectures including the sensitization with organic dyes that strongly absorb in the near infrared (NIR). In this work, we present a simple water-dispersible micellar system that features energy transfer from the novel NIR excitable dye, 1859 SL with a high molar absorption coefficient and a moderate fluorescence quantum yield to oleate-capped NaYF4:20%Yb(III), 2%Er(III) upconversion nanoparticles (UCNP) upon 808 nm excitation. The micelles were formed using the surfactants Pluronic F-127 and Tween 80 to produce a hydrophilic dye-UCNP system. Successful energy transfer from the dye to the UCNP could be confirmed by emission measurements that revealed the occurrence of upconversion emission upon excitation at 808 nm and an enhancement of the green Er(III) emission compared to direct Er(III) excitation at 808 nm.
Inorganic nanocrystals with linear and nonlinear luminescence in the ultraviolet, visible, near infrared and shortwave infrared like semiconductor quantum dots and spectrally shifting lanthanide-based nanophosphors have meanwhile found applications in the life and material sciences ranging from optical reporters for bioimaging and sensing over security barcodes to solid state lighting and photovoltaics. These nanomaterials commonly have increasingly sophisticated core/shell particle architectures with shells of different chemical composition and thickness to minimize radiationless deactivation at the particle surface that is usually the main energy loss mechanism [1]. For lanthanide-based spectral shifters, particularly for very small nanoparticles, also surface coatings are needed which protect near-surface lanthanide ions from luminescence quenching by high energy vibrators like O-H groups and prevent the disintegration of these nanoparticles under high dilution conditions. [2,3,4]. The identification of optimum particle structures requires quantitative spectroscopic studies focusing on the key performance parameter photoluminescence quantum yield [5,6], ideally flanked by single particle studies to assess spectroscopic inhomogeneities on a particle-to-particle level for typical preparation methods [7], Moreover, in the case of upconversion nanoparticles with a multi-photonic and hence, excitation power density (P)-dependent luminescence, quantitative luminescence studies over a broad P range are required to identify particle architectures that are best suited for applications in fluorescence assays up to fluorescence microscopy. Here, we present methods to quantify the photoluminescence of these different types of emitters in the vis/NIR/SWIR and as function of Pand demonstrate the importance of such measurements for a profound mechanistic understanding of the nonradiative deactivation pathways in semiconductor and upconversion nanocrystals of different size and particle architecture in different environments.
A solvothermal method was used to prepare a series of Yb3+/Tm3+/Ca2+ co-doped NaYF4 nanoparticles with different Ca2+ contents. Strong upconversion blue fluorescence could be observed under 980 nm laser excitation of the samples. The effect of different Ca2+ contents on the luminescence intensity was investigated, and it was found that the UV-vis upconversion luminescence increased and then decreased with an increasing Ca2+ concentration during the increase of the Ca2+ content from 0 mol% to 25 mol%, reaching the strongest fluorescence at 15 mol%, which was up to about 28 times stronger than that without Ca2+ doping. Furthermore, the mechanism was investigated, and it was found that the doping of Ca2+ disrupted the symmetry of the crystal field, resulting in a significant enhancement of the overall fluorescence. Applied to fluorescence intensity ratio thermometry, the absolute and relative sensitivities are as high as 0.0418 K−1 and 2.31% K−1, respectively, with a minimum temperature resolution of 0.0129 K.
Introduction. Comparing different emitter classes and rationally designing the next generation of molecular and nanoscale probes for bioimaging applications require accurate and quantitative methods for the measurement of the key parameter photoluminescence quantum yield f.1 f equals the number of emitted per number of absorbed photons. This is particularly relevant for increasingly used fluorescence imaging in the short wave-infrared region (SWIR) ≥ 900 nm providing deeper penetration depths, a better image resolution, and an improved signal-to-noise or tumor-to-background ratio.2, 3 However, spectroscopic measurements in the SWIR are more challenging and require specific calibrations and standards.
Relative and Absolute Methods for Measuring Photoluminescence Quantum Yields of UV/vis/NIR Emitters
(2019)
One of the key spectroscopic performance parameters of molecular and particulate emitters is the photoluminescence quantum yield (PL QY) that provides a direct measure for the number of emitted per absorbed photons. This triggered the interest in methods suitable for measuring this property for emitters in various environments in the UV/vis/NIR and above 1000 nm as well as on the ensemble and single emitter level. Moreover, for nonlinear emitters like lanthanide-based upconversion nanocrystals methods including instrumentation for power density-dependent PL QY studies are required.
An overview of the research activities in Division Biophotonics of BAM is given and suitable relative and absolute methods for the deter-mination of PL QY of organic dyes and different types of application-relevant nanomaterials in dispersion and in the solid state are presen-ted. This covers also the design and calibration of integrating sphere setups, achievable uncertainties, and candidates for PL QY reference materials.
In the blossoming field of Cd-free semiconductor quantum dots (QDs), ternary I–III–VI QDs have received increasing attention due to the ease of the environmentally friendly synthesis of high-quality materials in water, their high photoluminescence (PL) Quantum yields (QYs) in the red and near infrared (NIR) region, and their inherently low toxicity. Moreover, their oxygen-insensitive long PL lifetimes of up to several hundreds of nanoseconds close a gap for applications exploiting the compound-specific parameter PL lifetime. To overcome the lack of reproducible synthetic methodologies and to enable a design-based control of their PL properties, we assessed and modelled the synthesis of high-quality MPA-capped AgInS2/ZnS (AIS/ZnS) QDs. Systematically refined Parameters included reaction time, temperature, Ag:In ratio, S:In ratio, Zn:In ratio, MPA:In ratio, and pH using a design-of-experiment approach.
Guidance for the optimization was provided by mathematical models developed for the application-relevant PL parameters, maximum PL wavelength, QY, and PL lifetime as well as the elemental composition in terms of Ag:In:Zn ratio. With these experimental data-based models, MPA:In and Ag:In ratios and pH values were identified as the most important synthesis parameters for PL Control and an insight into the connection of these parameters could be gained. Subsequently, the experimental conditions to synthetize QDs with tunable emission and high QY were predicted. The excellent agreement between the predicted and experimentally found PL features confirmed the reliability of our methodology for the rational design of high quality AIS/ZnS QDs with defined PL features.
This approach can be straightforwardly extended to other ternary and quaternary QDs and to doped QDs.
We synthesized and characterized a set of ultrasmall hexagonal-phase NaGdF4: 20% Yb3+, 2% Er3+ upconversion nanoparticles with core diameters of 3.7 ± 0.5 nm. In order to assess passivation effects and the influence of possible core−shell intermixing and to identify optimum particle structures for combined imaging in the visible and near-infrared (vis−NIR: 410−850 nm) and short-wave infrared (SWIR: 1520 nm), NaYF4 shells of varying thicknesses (monolayer to 10 nm) were introduced and the influence of this parameter on the upconversion and downshifting photoluminescence of these particles was studied at different excitation power densities. This included excitation power-dependent emission spectra, slope factors, quantum yields, and excited state decay kinetics. These measurements revealed enhancement factors of the upconversion quantum yield of >10 000 in the low power region and an excitation power density-independent quantum yield of the downshifted emission at 1520 nm between 0.1 and 14%. The optimized shell thickness for combined vis and SWIR imaging was identified as 5 nm. Moreover, lifetimes and quantum yields can be continuously tuned by shell thickness which can be exploited for lifetime multiplexing and encoding. The fact that we did not observe a saturation of the upconversion quantum yield or the excited state decay kinetics with increasing shell thickness is ascribed to a strong intermixing of the active core with the inert shell during the shelling procedure. This indicates the potential of spectroscopic tools to detect cation intermixing.
Photodynamic therapy (PDT) used for treating cancer relies on the generation of highly reactive oxygen species, for example, singlet oxygen 1O2, by light-induced excitation of a photosensitizer (PS) in the presence of molecular oxygen, inducing DNA damage in close proximity of the PS. Although many precious metal complexes have been explored as PS for PDT and received clinical approval, only recently, the potential of photoactive complexes of nonnoble metals as PS has been discovered. Using the DNA origami technology that can absolutely quantify DNA strand break cross sections, we assessed the potential of the luminescent transition metal complex [Cr(ddpd)2]3+ (ddpd=N,N’-dimethyl-N,N’-dipyridine-2-ylpyridine-2,6-diamine) to damage DNA in an air-saturated aqueous environment upon UV/Vis illumination. The quantum yield for strand breakage, that is, the ratio of DNA strand breaks to the number of absorbed photons, was determined to 1–4%, indicating efficient transformation of photons into DNA strand breaks by [Cr(ddpd)2]3+.
Accurate and quantitative photoluminescence measurements are mandatory for the comparison of different emitter classes and the rational design of the next generation of molecular and nanoscale reporters as well as for most applications relying on their luminescence features in the life and material sciences and nanobiophotonics. In the following, procedures for the determination of the spectroscopic key parameter photoluminescence quantum yield, i.e., the number of emitted per absorbed photons, in the UV/vis/NIR/SWIR are presented including pitfalls and achievable uncertainties and material-specific effects related to certain emitter classes are addressed. Special emphasis is dedicated to luminescent nanocrystals.
Quantification of the Total and Accessible Number of Functional Groups and Ligands on Nanomaterials
(2022)
Surface-functionalized organic and inorganic nanoparticles (NP) are of great interest in the life and material sciences, as they can be used e.g. as drug carriers, fluorescent sensors, and multimodal labels in bioanalytical assays and imaging applications. NP performance in such applications depends not only on particle size, size distribution, and morphology, but also on surface chemistry, i.e. the total number of surface functional groups (FG) and the number of FG accessible for subsequent functionalization with ligands or biomolecules, which in turn determines surface charge, colloidal stability, biocompatibility, and toxicity. Methods for FG quantification should be simple, robust, reliable, fast, and inexpensive, and allow for the characteriza-tion of a broad variety of nanomaterials differing in size, chemical composition, and optical properties.
Aiming at the development of simple, versatile, and multimodal tools for the quantification of many bioanalytically relevant FG such as amine, carboxy, thiol and aldehyde functionalities, we investigated and compared various analytical methods commonly used for functional group quantification. This includes electrochemical titration methods, dye-based optical assays, and other instrumental analytical techniques such as nuclear magnetic resonance, mass spectrometry, and thermal analysis methods.
Engineered nanomaterials (NM) with their unique size-dependent properties are of increasing relevance for current and future developments in various fields such as medical and pharmaceutical industry, computing and electronics or food and consumer products. The performance and safety of NM are determined by the sum of their intrinsic physicochemical properties. Especially, the particle surface chemistry, which is largely controlled by the chemical nature and density of functional groups and ligands, is an important key driver for the performance, stability, and processibility of NM, as well as their interaction with the environment. Thus, methods for functional group quantification can foster the sustainable development of functional and safe(r) NM.
Aiming at the development of simple, versatile and multimodal tools for the quantification of common bioanalytically relevant functional groups, we designed a catch-and-release assay based on cleavable probes that enable the quantification of the cleaved-off reporters in the supernatant after particle separation. Thus, the approach circumvents interferences resulting from particle light scattering and sample-inherent absorption or emission. To study the potential of the assay, commercially available and in-house synthesized aminated and carboxylated polymer and silica nanoparticles of different functional group densities were tested.
Our cleavable probe strategy can be easily adapted to other analytical techniques requiring different reporters, or to different types of linkers that can be cleaved thermally, photochemically, or by variation of pH, utilizing well-established chemistry. In addition, it can contribute to the development of multi-method characterization strategies to provide a more detailed picture of the intrinsic physicochemical property - performance/safety relationships and thus can support the design of tailored nanomaterials with better controlled properties.
Lanthanide-based upconversion nanoparticles (UCNPs) like hexagonal Beta-NaYF4 UCNPs doped with Yb3+ and Er3+, which efficiently convert 976 nm light to ultraviolet, visible, and near infrared photons, offer new strategies for luminescence-based sensing, barcoding, and imaging. The properties of their upconversion (UC) luminescence (UCL) are, however, strongly influenced by particle size, the concentration and spatial arrangement of the dopant ions, surface chemistry including presence and thickness of surface passivation and shielding shells, microenvironment/presence of quenchers with high energy vibrations, and excitation power density (P). We present here a comprehensive study of the influence of UCNP size and particle architecture for Yb3+ and Er3+ co-doped NaYF4 core-only and core-shell nanostructures in the size range of about 5 nm to 50 nm, which underlines the importance of particle synthesis, surface chemistry, and quantitative luminescence measurements for mechanistic insights and the determination of application-relevant matrix- and P-dependent optimum dopand concentrations.
Aldehyde moieties on 2D-supports or microand nanoparticles can function as anchor groups for the attachment of biomolecules or as reversible binding sites for proteins on cell surfaces. The use of aldehyde-based materials in bioanalytical and medical settings calls for reliable methods to detect and quantify this functionality. We report here on a versatile concept to quantify the accessible aldehyde moieties on particle surfaces through the specific binding and subsequent release of small reporter molecules such as fluorescent dyes and nonfluorescent chromophores utilizing acylhydrazone formation as a reversible covalent labeling strategy. This is representatively demonstrated for a set of polymer microparticles with different aldehyde labeling densities. Excess reporter molecules can be easily removed by washing, eliminating inaccuracies caused by unspecific adsorption to hydrophobic surfaces. Cleavage of hydrazones at acidic pH assisted by a carbonyl trap releases the fluorescent reporters rapidly and quasi-quantitatively and allows for their fluorometric detection at low concentration. Importantly, this strategy separates the signal-generating molecules from the bead surface. This circumvents common issues associated with light scattering and signal distortions that are caused by binding-induced changes in reporter fluorescence as well as quenching dye−
dye interactions on crowded particle surfaces. In addition, we demonstrate that the release of a nonfluorescent chromophore via disulfide cleavage and subsequent quantification by absorption spectroscopy gives comparable results, verifying that both assays
are capable of rapid and sensitive quantification of aldehydes on microbead surfaces. These strategies enable a quantitative
comparison of bead batches with different functionalization densities, and a qualitative prediction of their coupling efficiencies in bioconjugations, as demonstrated in reductive amination reactions with Streptavidin.
The NaYF4: Yb3+/Tm3+@NaYF4@β-CD upconversion nanoparticles were successfully prepared by the solvothermal method, and the samples were pure hexagonal phase with good crystallinity and homogeneous size, asevidenced by XRD and TEM analysis. The FT-IR analysis shows that β-CD is successfully encapsulated on the surface of NaYF4: Yb3+/Tm3+@NaYF4 nanoparticles. The fluorescence intensity 3and lifetime were significantly increased after coating the inert layer on the surface of core nanoparticles. After further surface modification of β-CD, the fluorescence intensity and fluorescence lifetime were reduced, but the overall fluorescence was stronger. Temperature measurements using the fluorescence intensity ratio technique were found to have relatively low reliability and absolute sensitivity for temperature measurements using thermally coupled energy levels. However, the reliability of temperature measurements using non-thermally coupled energy levels is significantly higher and the absolute sensitivity is much higher than for measurements at thermally coupled levels. Since the maximum absolute sensitivity, maximum relative sensitivity and minimum temperature resolution are determined to be 0.1179 K-1, 2.19 %K 1 and 0.00019 K, respectively, NaYF4: Yb3+/Tm3+@NaYF4@β-CD upconversion nanoparticles are expected to be widely used in the biomedical field due to their feasibility, reliability, non-toxicity and harmlessness.
A series of NaYF4:Yb3+/Tm3+@NaYF4:Yb3+/Er3+ nanoparticles doped with Tm3+ and Er3+ were successfully prepared by the solvothermal method. Under 980 nm laser excitation, intense upconversion emission peaks of Tm3+ and Er3+ were observed for all samples. By doping Tm3+ and Er3+ with core–shell partitioning, not only a significant increase in fluorescence intensity could be achieved, but also simultaneous temperature measurements on multiple thermocouple energy levels could be realised. In addition, the temperature sensing performance of different thermocouple energy levels was also investigated, and it was found that the 3 F3 → 3 H6 and 1 G4 → 3 F4 thermocouple energy level pairs of Tm3+ were the best, with maximum absolute sensitivity and maximum relative sensitivity of up to 0.0250 K−1 and 2.155% K−1 respectively, higher than the sensitivity of other thermocouple energy levels. It has a temperature resolution of less than 0.0139 K, which is lower than that of most materials available today. By using this material as a probe to build a fiber optic temperature sensor platform, it was found to have reliable temperature measurement performance.
Extracellular vesicles (EV) are cell-derived particles in body fluids, which have excellent potential as next-generation biomarkers. The exploitation of EV requires reliable measurements, which is currently very difficult, as most EV are smaller than 200 nm. At present, flow cytometry (FCM) is the most appropriate technique for EV analysis in biological samples, as FCM is readily available in many clinical laboratories and allows to identify cell-specific EV at high throughput. However, due to technical variations between different FCM instruments, EV concentration measurements are currently not well comparable between most laboratories. Therefore, EV reference materials and standardized reference methods are urgently needed to calibrate flow rate, light scattering intensity, and fluorescence intensity of FCM in the sub-micrometer size range. This requires a better matching of the optical properties of calibration beads and EV as can be realized with current polystyrene calibration beads.
The EMPIR project 18HLT01 “MetVes II” aims to develop synthetic reference materials and traceable measurement methods to standardize EV measurements. The reference materials should resemble EV properties, so that calibrations are reliable and do not require a change of acquisition settings. Hence, the reference materials should contain particles with a traceable number concentration in the range of 109–1012 particles/mL to calibrate flow rate, a traceable size with discrete diameters between 50–1000 nm and a refractive index (RI) in the range of 1.37–1.42 to calibrate scattering intensity, and a traceable fluorescence intensity between 100–100,000 molecules of equivalent soluble fluorochromes (MESF). At BAM, various approaches to prepare such low-RI nanometer-sized reference materials will be studied, preliminary results of the primary characterization of these candidate reference particles will be presented, and possible applications besides FCM-based EV detection will be outlined.
Photoluminescence Quantum Yields of Luminescent Nanocrystals and Particles in the UV/vis/NIR/SWIR
(2023)
The rational design of functional luminescent materials such as semiconductor quantum dots and lanthanide-based upconversion nanoparticles, all photophysical and mechanistic studies, and the comparison of different emitters require accurate and quantitative photoluminescence measurements. Particularly the reliable determination of the key performance parameter photoluminescence quantum yield (f), the number of emitted per absorbed photons, and the brightness are of special importance for luminescence applications in the life and material sciences and nano(bio)photonics.[1] In this context, examples for absolute measurements of the photoluminescence quantum yields of UV/vis/NIR/SWIR emissive semiconductor quantum dots and rods, made from different materials, and spectrally shifting lanthanide upconversion nanocrystals with different surface chemistries in transparent matrices are presented including excitation wavelength and power density dependent studies utilizing integration sphere spectroscopy.[2,3] In addition, procedures for the absolute determination of the photoluminescence quantum yields of scattering dispersions of larger size quantum rods and differently sized inorganic particles have been developed as well as procedures for the characterization of solid luminescent nanomaterials such as different perovskites and YAG:Cer converter materials.[4] Thereby, challenges and pitfalls of f measurements in different wavelength regions including the SWIR and material-specific effects related to certain emitter classes are addressed, achievable uncertainties are quantified, and relative and absolute measurements of photoluminescence quantum yield measurements are compared to underline limitations of the former approach. Finally, a set of novel UV/vis/NIR quantum yield standards is presented including their certification with a complete uncertainty budget.[5]
Correlating the photoluminescence (PL) properties of nanomaterials like semiconductor nanocrystals (QDs) and upconversion nanocrystals (UCNPs) assessed in ensemble studies and at the single particle level is increasingly relevant for applications of these nanomaterials in the life sciences like bioimaging studies or their use as reporters in microfluidic assays. Here we present a comparison of the spectroscopic properties of ensembles and single emitters for QDs like II/VI QDs and cadmium-free AIS/ZnS QDs as well as different UCNPs. The overall goal of this study was to derive particle architectures well suited for spectroscopic and microscopic applications.
Cd-free I–III–VI group semiconductor quantum dots (QDs) like Ag–In–S and Cu–In–S show unstructured absorption spectra with a pronounced Urbach tail, rendering the determination of their band gap energy (Eg) and the energy structure of the exciton difficult. Additionally, the origin of the broad photoluminescence (PL) band with lifetimes of several hundred nanoseconds is still debated. This encouraged us to study the excitation energy dependence (EED) of the PL maxima, PL spectral band widths, quantum yields (QYs), and decay kinetics of AIS/ZnS QDs of different size, composition, and surface capping ligands. These results were then correlated with the second derivatives of the corresponding absorption spectra. The excellent match between the onset of changes in PL band position and spectral width with the minima found for the second derivatives of the absorption spectra underlines the potential of the EED approach for deriving Eg values of these ternary QDs from PL data. The PL QY is, however, independent of excitation energy in the energy range studied. From the EED of the PL features of the AIS/ZnS QDs we could also derive a mechanism of the formation of the low-energy electronic structure. This was additionally confirmed by a comparison of the EED of PL data of as-synthesized and size-selected QD ensembles and the comparison of these PL data with PL spectra of single QDs. These results indicate a strong contribution of intrinsic inhomogeneous PL broadening to the overall emission features of AIS/ZnS QDs originating from radiative transitions from a set of energy states of defects localized at different positions within the quantum dot volume, in addition to contributions from dimensional and chemical broadening. This mechanism was confirmed by numerically modelling the absorption and PL energies with a simple mass approximation for spherical QDs and a modified donor–acceptor model, thereby utilizing the advantages of previously proposed PL mechanisms of ternary QDs. These findings will pave the road to a deeper understanding of the nature of PL in quantum confined I–III–VI group semiconductor nanomaterials.
Photoluminescence applications in the life and material sciences require bright molecular and nanocrystalline emitters, stimuli-responsive optical probes, signal enhancement, multiplexing, and barcoding strategies and traceable methods to quantify the signal-relevant optical properties of luminescent materials at the ensemble and single molecule/particle level. In this context, current research at Division Biophotonics of BAM is presented ranging from dye and nanocrystal photophysics, absolute measurements of photoluminescence quantum yields in the UV/vis/NIR/SWIR, lifetime multiplexing, and the development of different types of fluorescence standards for validating optical-spectroscopic measurements.
Optical pH sensors utilizing colorimetric or fluorescent indicator dyes are highly promising in many biomedical and life science applications where electrochemical sensors fail. For instance, optical sensors are not prone to electrical interferences, they are noninvasive and enable remote measurements. Moreover, fluorescence detection is very fast, highly sensitive, and provides several readout parameters ideal for multiplexing with nanometer resolution using simple, inexpensive, and miniaturizable instrumentation. Here, we present the design of a dyad sensor molecule, consisting of an analyte-responsive and an analyte inert reference fluorophore.
Singlet oxygen can severely damage biological tissue, which is exploited in photodynamic therapy (PDT). In PDT, the effective range is limited by the distribution of the photosensitizer (PS) and the illuminated area. However, no distinction is made between healthy and pathological tissue, which can cause undesired damage. This encouraged us to exploit the more acidic pH of cancerous tissue and design pH-controllable singlet oxygen-generating boron-dipyrromethene (BODIPY) dyes. A pH sensitivity of the dyes is achieved by the introduction of an electronically decoupled, photoinduced electron transfer (PET)-capable subunit in meso-position of the BODIPY core. To favor triplet-state formation as required for singlet Oxygen generation, iodine substituents were introduced at the chromophore core. The resulting pH-controlled singlet oxygen-generating dyes with pKa values in the physiological range were subsequently assessed regarding their potential as pH-controlled PS for PDT.
Using HeLa cells, we could successfully demonstrate markedly different pH-dependent cytotoxicities upon illumination.
In recent years, the demand for reliable, versatile, fluorescent pH and oxygen sensors has increased rapidly in many biomedical applications since these analytes are important indicators of cell function or certain diseases. Therefore, sensor particles are needed that are small enough to penetrate cells, non-toxic, and allow for close-up optical monitoring. When developing such sensor systems, one must consider the pH and oxygen range detectable by the sensor dye and the matrix material of the used carrier particles. Here, we present the development of pH- and oxygen-responsive polymeric beads functionalized with fluorescent dyad molecules that consist of an analyte-responsive fluorophore and an analyte-inert dye.
Neuartige Materialien, die bekannte (Werk-)Stoffe mit neuen Funktionalitäten ausstatten, spielen eine zunehmend wichtige Rolle im Bereich der Materialforschung und -prüfung. Das Spektrum neuartiger Materialien reicht von der gezielten Oberflächenfunktionalisierung und -strukturierung makroskopischer Materialien, dünnen Beschichtungen bis hin zu mikro- und nanoskaligen Kompositmaterialien und funktionalen Materialien an der Schnittstelle zur Biologie, Biotechnologie, nachhaltige Energiespeicherung und Sensorik. Dabei bieten neuartige Materialien die Chance, Werkstoffe und Produkte mit erweiterter oder verbesserter Funktionalität zu erhalten und Sicherheit bereits im Designprozess zu berücksichtigen. Durch dieses breite Anwendungsspektrum und die Herausforderungen, die solche Materialien für die Sicherheit in Chemie und Technik mit sich bringen, sind diese in allen Themenfeldern der BAM repräsentiert (Material, Analytical Sciences, Energie, Infrastruktur und Umwelt).
Die Aufgaben der BAM erstrecken sich dabei von der Herstellung von Referenzmaterialien für Industrie, Forschung und Regulation, über die Erstellung von standardisierten Referenzverfahren für nachhaltige Messungen im Umwelt- und Lebenswissenschaftsbereich bis hin zur Bereitstellung von belastbaren und zitierbaren Referenzdaten. Durch die genaue Charakterisierung neuartiger Materialien können potentiell problematische Substanzen identifiziert und deren Risiken besser abgeschätzt werden. In diesem Beitrag werden einige aktuelle Beispiele aus diesen Bereichen vorgestellt.
A brief perspective of BAM on advanced materials is presented including examples for nanomaterials and other systems presenting advanced materials with special emphasis on characterization methods used in different division of BAM for the determination of functional or safety parameters of such materials. In this respect, also ongoing activities of the capacity building project nanoplatform of BAM aiming at the development of nanometer-sized reference materials are briefly summarized.
A systematic study of the luminescence properties of monodisperse β-NaYF4: 20% Yb3+, 2% Er3+ upconversion nanoparticles (UCNPs) with sizes ranging from 12–43 nm is presented utilizing steady-state and time-resolved fluorometry.
Special emphasis was dedicated to the absolute quantification of size- and environment-induced quenching of upconversion luminescence (UCL) by highenergy O–H and C–H vibrations from solvent and ligand molecules at different excitation power densities (P). In this context, the still-debated Population pathways of the 4F9/2 energy level of Er3+ were examined. Our results Highlight the potential of particle size and P value for color tuning based on the pronounced near-infrared emission of 12 nm UCNPs, which outweighs the red Er3+ emission under “strongly quenched” conditions and accounts for over 50% of total UCL in water. Because current rate equation models do not include such emissions, the suitability of these models for accurately simulating all (de)population pathways of small UCNPs must be critically assessed. Furthermore, we postulate population pathways for the 4F9/2 energy level of Er3+, which correlate with the size-, environment-, and P-dependent quenching states of the higher Er3+ energy levels.
Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, and catalysts.
Loading content and release kinetics of these compounds are controlled by type and number of hydrophobic groups in the amphiphilic copolymer network. Thus, understanding the interactions between cargo and colloidal carrier is mandatory for a tailor-made and cargo-specific ANG design. To systematically explore the influence of the network composition on these interactions, we prepared a set of ANGs of different amphiphilicity and loaded these ANGs with varying concentrations of the solvatochromic dye Nile Red (NR). Here, NR acts as a hydrophobic model cargo to optically probe the polarity of its microenvironment. Analysis of the NR emission spectra as well as measurements of the fluorescence quantum yields and decay kinetics revealed a decrease in the polarity of the NR microenvironment with increasing hydrophobicity of the hydrophobic groups in the ANG network and dye–dye interactions at higher loading concentrations. At low NR concentrations, the hydrophobic cargo NR is encapsulated in the hydrophobic domains. Increasing NR concentrations resulted in probe molecules located in a more hydrophilic environment, i.e., at the nanodomain border, and favored dye–dye interactions and NR aggregation.
These results correlate well with release experiments, indicating first NR release from more hydrophilic network locations. Overall, our findings demonstrate the importance to understand carrier–drug interactions for efficient loading and controlled release profiles in amphiphilic nanogels.
Optical spectroscopy – Techniques, instrumentation, and typical molecular and nanoscale reporters
(2018)
Different types of optical spectroscopies are introduced with special emphasis on method-inherent limitations and reliable instrument calibration and performance validation. In addition, different classes of molecular and nanocrystalline emitters are presented and the underlying photophysical processes are briefly described.
Merocyanine–triarylamine bichromophores are readily synthesized by sequentially Pd-catalyzed insertion alkynylation–Michael–Suzuki four-component reactions. White-light emissive systems form upon aggregation in 1 : 99 and 0.1 : 99.9 vol% CH2Cl2–cyclohexane mixtures, ascribed to aggregation-induced dual emission (AIDE) in combination with partial energy transfer between both chromophore units as supported by spectroscopic studies.
The unique optoelectronic properties of semiconductor nanocrystals, also termed quantum dots (QDs), have led to many advances in optoelectronic devices, bioimaging, and biosensing. This strong potential in a wide range of applications sparked the interest for a better understanding of the QD formation mechanisms. Recent studies have shown that atomically defined, zero-dimensional magic-size clusters (MSCs) play a crucial role during the nucleation and growth of QDs. Thereby MSCs consist of discrete numbers of ions leading to narrow size distributions and thus narrow absorption peaks, which evolve in discrete steps from one stable size to the next. The formation of MSCs was found in the synthesis of II-VI and III-V QDs but only limited synthesis approaches are available for the synthesis of MSCs in single-ensemble form without coexistence of other-size QDs. These MSCs can further self-assemble into two- and three-dimensional hybrid structures using organic ligands like diamines, leading to enhanced photoluminescence properties and catalytic activities.
In this contribution, we present a synthesis strategy for the preparation of single-sized ZnSe MSCs. With a band gap of 2.7 eV and being an earth-abundant material, ZnSe QDs are interesting for light-emitting devices, blue-green lasers, photocatalysis, and fluorescence probes. In contrast to other studies, our approach is based on a one-pot heat-up synthesis and uses less toxic and dangerous zinc precursors (e.g. zinc stearate). Knowing that thiol-based ligands can alter the formation process of ZnSe QDs, we investigated the influence of 1-dodecanethiol on the ZnSe MSC formation using absorption spectroscopy, TEM, XPS, and XRD. By variation of the thiol ligand concentration and reaction temperature, we were able to synthesize two new ZnSe MSC sizes, the largest so far, by using easy-to-handle precursors.
Tailor-made nanoparticles are of increasing interest in e.g. catalysis, as sensor materials, analytical assays, or can have superior photophysical properties. A major issue concerning the preparation of high-quality and functional nanoparticles is a good control of particle size, shape, polydispersity, and composition.
Small Angle X-ray Scattering (SAXS) is a non-destructive method for the analysis of nanostructures in a wide variety of materials. This method allows determining averaged structural parameters on a length scale from just above atomic sizes up to several 100 nanometers such as sizes, size distributions, volume fractions, and inner surface sizes. Moreover, anomalous Small Angle X-ray Scattering (ASAXS) exploits the anomalous dispersion of the scattering amplitudes near the X-ray absorption edges of the elements contained in the sample. These element sensitive contrast variations can be used to analyse average composition fluctuations on the nm scale. Two kinds of nanoparticles are chosen here to elaborate the advantages of ASAXS in the analysis of complex materials.
A facile and efficient methodology is developed for the thermal synthesis of size-tunable, stable, and uniform bimetallic NiCu core–shell nanoparticles (NPs) for various application in catalysis. Their diameter can be tuned in a range from 6 nm to 30 nm and the Ni:Cu ratio is adjustable in a wide range from 1:1 to 30:1. The NPs are structurally characterized by a method combination of transmission electron microscopy, anomalous small-angle X-ray scattering (ASAXS), X-ray absorption fine structure, and X-ray photoelectron spectroscopy. Here, we focus on the ASAXS method and its ability to analyses nanostructure parts and their compositions at once. As a result, a NiCu alloyed core surrounded by a Ni enriched shell and an outer NiO shell was found.
Semiconductor nanocrystals (quantum dots, QDs) are well known for their superior photophysical properties and enabled advancements in several key technologies of the 21st century and numerous technological applications like in photovoltaics, LED displays, photocatalysis, and biosensing. To achieve high photoluminescence quantum yields (PLQY) and enhanced photostability the QD core needs to be passivated by a second semiconductor, which possess a larger band gap to confine the charges within the QD core. An important parameter is thereby the lattice mismatch between the core and shell. To avoid strong lattice strain, which would alter the photophysical properties, an intermediary shell can be used as a lattice adapter between the core and the outer shell leading to core/shell/shell systems. These systems have shown to possess high PLQYs combined with a strong long-term stability and can be found in modern QLED displays. ASAXS was used here to better understand the core/shell/shell structure of InP/ZnSe/ZnS QDs to enable a correlation between their structural and photophysical properties.
In this study, we systematically investigate the decay characteristics of upconversion luminescence (UCL) under anti-Stokes excitation through numerical simulations based on rate-equation models. We find that a UCL decay profile generally involves contributions from the sensitizer’s excited-state lifetime, energy transfer and cross-relaxation processes. It should thus be regarded as the overall temporal response of the whole upconversion system to the excitation function rather than the intrinsic lifetime of the luminescence emitting state. Only under certain conditions, such as when the effective lifetime of the sensitizer’s excited state is significantly shorter than that of the UCL emitting state and of the absence of cross-relaxation processes involving the emitting energy level, the UCL decay time approaches the intrinsic lifetime of the emitting state. Subsequently, Stokes excitation is generally preferred in order to accurately quantify the intrinsic lifetime of the emitting state. However, possible cross-relaxation between doped ions at high doping levels can complicate the decay characteristics of the luminescence and even make the Stokesexcitation approach fail. A strong cross-relaxation process can also account for the power dependence of the decay characteristics of UCL.
Photonen-Aufkonvertierung in hetero-oligonuklearen, Metallkomplex-Architekturen mit organischen Liganden ist ein interessantes, aber bisher selten beobachtetes Phänomen, trotz des großen Potentials sowohl aus Sicht der Grundlagenforschung als auch aus der Anwendungsperspektive. Nun wurde ein neues photonisches Material aus molekularen Chrom(III)- und Ytterbium(III)-Komplexionen entwickelt.
Dieses zeigt im Festkörper bei Raumtemperatur abhängig von der Anregungsleistungsdichte nach Anregung des 2F7/2! 2F5/2-3berganges des Ytterbiums bei ca. 980 nm eine kooperative Sensibilisierung der Chrom(III)-zentrierten 2E/2T1-Phosphoreszenz bei ca. 775 nm. Der Aufkonvertierungsprozess ist unempfindlich gegenüber Luftsauerstoff und kann in Gegenwart von Wassermolekülen im Kristallgitter beobachtet werden.
Using fluorescence-guided surgery (FGS) to cytoreductive surgery helps achieving complete resection of microscopic ovarian tumors. The use of visible and NIR-I fluorophores has led to beneficial results in clinical trials; however, involving NIR-II dyes seems to outperform those benefits due to the deeper tissue imaging and higher signal/noise ratio attained within the NIR-II optical window. In this context, we developed NIR-II emitting dyes targeting human epidermal growth factor receptor 2 (HER2)-positive ovarian tumors by coupling water-soluble NIR-II aza-BODIPY dyes to the FDA-approved anti-HER2 antibody, namely, trastuzumab. These bioconjugated NIR-II-emitting dyes displayed a prolonged stability in serum and a maintained affinity toward HER2 in vitro. We obtained selective targeting of HER2 positive tumors (SKOV-3) in vivo, with a favorable tumor accumulation. We demonstrated the fluorescence properties and the specific HER2 binding of the bioconjugated dyes in vivo and thus their potential for NIR-II FGS in the cancer setting.
Boron neutron capture therapy (BNCT) relies on the activation of 10B by thermal neutrons, which results in small highly energetic particle emission inducing cancer cells damage. However, in order to overcome the limits of the currently used BNCT agents, it is necessary to design new systems, which can specifically accumulate and deliver a sufficient amount of 10B in tumors. In this study, we designed a 10B-BSH-containing aza-BODIPY (aza-SWIR-BSH). It enabled the efficient vectorization of clinically used 10B-BSH to the tumor, resulting in higher therapeutic activity than the 10B-BSH alone.
Luminescence techniques are amongst the most commonly used analytical methods in the life and material sciences due to their high sensitivity and non-destructive and multiparametric character. Photoluminescence signals are, however, affected by wavelength-, polarization-, and time-dependent instrument specific effect and the compound-specific photoluminescence quantum yield. The former hamper the comparability of fluorescence measurements, while the relative determination of the latter requires suitable quantum yield standards with well-known photoluminescence quantum yields (QY). For the simple correction of instrument specific effects in the wavelength region of 300 nm to 950 nm, the set of the five certified spectral fluorescence standards BAM-F001 – BAM-F005, has been extended to the NIR range by including two new fluorescence standards currently under certification. For the reliable and accurate determination of QY which is the key performance parameter for the comparison of different luminophores, we certified a set of 12 quantum yield standards, which absorb and emit in the wavelength range from 300 nm to 1000 nm.
The surface chemistry of nanomaterials controls their interaction with the environment and biological species and their fate and is hence also relevant for their potential toxicity. This has meanwhile led to an increasing interest in validated and preferably standardized methods for the determination and quantification of surface functionalities on nanomaterials and initiated different standardization projects within ISO/TC 229 and IEC/TC 113 as well as interlaboratory comparisons (ILCs) of different analytical methods for the quantification of surface coatings by OECD. Here we present the results of a first ILC on the quantification of the amount of amino functionalities on differently sized inorganic nanoparticles done by division Biophotonics and the National Research Council of Canada (NRC) and the PWI 19257 on the Characterization and Quantification of Surface Functional Groups and Coatings on Nanoobjects approved by ISO/TC 229 (WG2) in fall 2022 that will result in a VAMAS study on this topic organized by division Biophotonics. Key words: nanoparticles, surface analysis, surface functional groups, quantification, optical assay, qNMR, VAMAS, standardization, ICL, quality assurance, reference material.
Upconversion photoluminescence in hetero-oligonuclear metal complex architectures featuring organic ligands is an interesting but still rarely observed phenomenon, despite its great potential from a basic research and application perspective. In this context, a new photonic material consisting of molecular chromium(III) and ytterbium(III) complex Ions was developed that exhibits excitation-power density-dependent cooperative sensitization of the chromium-centered 2E/2T1 phosphorescence at approximately 775 nm after excitation of the ytterbium band 2F7/2!2F5/2 at approximately 980 nm in the solid state at ambient temperature. The upconversion process is insensitive to atmospheric oxygen and can be observed in the presence of water molecules in the crystal lattice.
The core−shell NaYF4:Yb3+/Tm3+@NaYF4:Yb3+ upconversion nanoparticles were successfully prepared by a solvothermal method, and a layer of mesoporous silica (mSiO2) was successfully coated on the periphery of the core−shell nanoparticles to transform their surface from lipophilic to hydrophilic, further expanding their applications in biological tissues. The physical phase, morphology, structure, and fluorescence properties were characterized by X-ray diffraction (XRD), field emission transmission electron microscopy (TEM), Fourier infrared spectroscopy (FT-IR), ζ potential analysis, and fluorescence spectroscopy. It was found that the material has a hexagonal structure with good hydrophilicity and emits intense fluorescence under 980 nm pump laser excitation. The non-contact temperature sensing performance of nanoparticles was evaluated by analyzing the upconversion fluorescence of Tm3+ (1G4 → 3F4 and 3F3 → 3H6) in the temperature range of 284−344 K. The absolute and relative sensitivities were found to be 0.0067 K−1 and 1.08 % K−1, respectively, with high-temperature measurement reliability and good temperature cycling performance. More importantly, its temperature measurement in phosphate-buffered saline (PBS) solution is accurate. In addition, the temperature of the cells can be increased by adjusting the laser power density and laser irradiation time. Therefore, an optical temperature sensing platform was built to realize the application of real-time monitoring of cancer cell temperature and the dual function of photothermal therapy.
Upconversion core/shell nanocrystals with different mean sizes ranging from 15 to 45 nm were prepared via a modified synthesis procedure based on anhydrous rare‐earth acetates. All particles consist of a core of NaYF4:Yb,Er, doped with 18 % Yb3+ and 2 % Er3+, and an inert shell of NaYF4, with the shell thickness being equal to the radius of the core particle. Absolute measurements of the photoluminescence quantum yield at a series of different excitation power densities show that the quantum yield of 45 nm core/shell particles is already very close to the quantum yield of microcrystalline upconversion phosphor powder. Smaller core/shell particles prepared by the same method show only a moderate decrease in quantum yield. The quantum yield of 15 nm core/shell particles, for instance, is reduced by a factor of three compared to the bulk upconversion phosphor at high power densities (100 W cm−2) and by approximately a factor of 10 at low power densities (1 W cm−2).
What to measure? is a key question in nanoscience, and it is not straightforward to address as different physicochemical properties define a nanoparticle sample. Most prominent among these properties are size, shape, surface charge, and porosity. Today researchers have an unprecedented variety of measurement techniques at their disposal to assign precise numerical values to those parameters. However, methods based on different physical principles probe different aspects, not only of the particles themselves, but also of their preparation history and their environment at the time of measurement. Understanding these connections can be of great value for interpreting characterization results and ultimately controlling the nanoparticle structure–function relationship. Here, the current techniques that enable the precise measurement of these fundamental nanoparticle properties are presented and their practical advantages and disadvantages are discussed. Some recommendations of how the physicochemical parameters of nanoparticles should be investigated and how to fully characterize these properties in different environments according to the intended nanoparticle use are proposed. The intention is to improve comparability of nanoparticle properties and performance to ensure the successful transfer of scientific knowledge to industrial real‐world applications.
Nanomaterials are used in many different applications in the material and life sciences. Examples are optical reporters, barcodes, and nanosensors, magnetic and optical contrast agents, and catalysts. Due to their small size and large surface area, there are also concerns about their interaction with and uptake by biological systems. This has initiated an ever increasing number of cyctoxicity studies of nanomaterials of different chemical composition and surface chemistry, but until now, the toxicological results presented by different research groups often do not address or differ regarding a potential genotoxicity of these nanomaterials. This underlines the need for a standardized test procedure to detect genotoxicity.1,2
Aiming at the development of fast, easy to use, and automatable microscopic methods for the determination of the genotoxicity of different types of nanoparticles, we assess the potential of the fluorometric γH2AX assay for this purpose. This assay, which can be run on an automated microscopic detection system, relies on the determination of DNA double strand breaks as a sign for genotoxicity.3 Here, we present first results obtained with broadly used nanomaterials like CdSe/CdS and InP/ZnS quantum dots as well as iron oxide, gold, and polymer particles of different surface chemistry with previously tested colloidal stability. These studies will be also used to establish nanomaterials as positive and negative genotoxicity controls or standards for assay performance validation for users of this fluorometric genotoxicity assay. In the future, after proper validation, this microscopic platform technology will be expanded to other typical toxicity assays.
References. (1) Landsiedel, R.; Kapp, M. D.; Schulz, M.; Wiench, K.; Oesch, F., Reviews in Mutation Research 2009, 681, 241-258. (2) Henriksen-Lacey, M.; Carregal-Romero, S.; Liz-Marzán, L. M., Bioconjugate Chem. 2016, 28, 212-221. (3) Willitzki, A.; Lorenz, S.; Hiemann, R.; Guttek, K.; Goihl, A.; Hartig, R.; Conrad, K.; Feist, E.; Sack, U.; Schierack, P., Cytometry Part A 2013, 83, 1017-1026.
Organic and inorganic nanoparticles (NPs) are increasingly used as drug carriers, fluorescent sensors, and multimodal labels in the life and material sciences. These applications require knowledge of the chemical nature, total number of surface groups, and the number of groups accessible for subsequent coupling of e.g., antifouling ligands, targeting bioligands, or sensor molecules. To establish the concept of catch-and-release assays, cleavable probes were rationally designed from a quantitatively cleavable disulfide moiety and the optically detectable reporter 2-thiopyridone (2-TP). For quantifying surface groups on nanomaterials, first, a set of monodisperse carboxy-and amino-functionalized, 100 nm-sized polymer and silica NPs with different surface group densities was synthesized. Subsequently, the accessible functional groups (FGs) were quantified via optical spectroscopy of the cleaved off reporter after its release in solution. Method validation was done with inductively coupled plasma optical emission spectroscopy (ICP-OES) utilizing the sulfur atom of the cleavable probe. This comparison underlined the reliability and versatility of our probes, which can be used for surface group quantification on all types of transparent, scattering, absorbing and/or fluorescent particles. The correlation between the total and accessible number of FGs quantified by conductometric titration, qNMR, and with our cleavable probes, together with the comparison to results of conjugation studies with differently sized biomolecules reveal the potential of catch-and-release reporters for surface analysis. Our findings also underline the importance of quantifying particularly the accessible amount of FGs for many applications of NPs in the life sciences.
Multifunctional efficiency: Extending the concept of atom economy to functional nanomaterials
(2018)
Green chemistry, in particular, the principle of atom economy, has defined new criteria for the efficient and sustainable production of synthetic compounds. In complex nanomaterials, the number of embedded functional entities and the energy expenditure of the assembly process represent additional compound-associated parameters that can be evaluated from an economic viewpoint. In this Perspective, we extend the principle of atom economy to the study and characterization of multifunctionality in nanocarriers, which we define as “multifunctional efficiency”. This concept focuses on the design of highly active nanomaterials by maximizing integrated functional building units while minimizing inactive components. Furthermore, synthetic strategies aim to minimize the number of steps and unique reagents required to make multifunctional nanocarriers. The ultimate goal is to synthesize a nanocarrier that is highly specialized but practical and simple to make. Owing to straightforward crystal engineering, metal−organic framework (MOF) nanoparticles are an excellent example to illustrate the idea behind this concept and have the potential to emerge as next-generation drug delivery systems. Here, we highlight examples showing how the combination of the properties of MOFs (e.g., their organic−inorganic hybrid nature, high surface area, and biodegradability) and induced systematic modifications and functionalizations of the MOF’s scaffold itself lead to a nanocarrier with high multifunctional efficiency.
In recent years, the use of functionalized micro- and nanomaterials has increased rapidly for a wide range of applications in the life and material sciences, due to their unique properties in combination with their high surface-to-volume ratio and stability. For instance, functionalized micro- and nanomaterials, that are labeled or stained with a multitude of sensor dyes can be used for monitoring, and quantification of neutral and ionic analytes. These materials have several advantages as compared to conventional molecular probes like enhanced brightness, ease of designing ratiometric systems by combining analyte-sensitive and inert reference dyes, and increased photostability. Moreover, stained nanoparticles can enable the use of hydrophobic dyes in aqueous environments.
Versatile templates and carriers for the fabrication of nanosensors by staining and/or labeling with different fluorophores and sensor molecules are biocompatible silica and polymeric particles, because they can be synthesized in large scales at low costs with different surface chemistries.
Here we present our work on multicolored sensors for the measurement of pH, oxygen and saccharides utilizing commercially available or in-house synthesized silica and polymeric particles.
A first tricolor fluorescent pH nanosensor is presented, which was rationally designed from biocompatible carboxylated polystyrene nanoparticles and two analyte-responsive molecular fluorophores. Its fabrication involved particle staining with a blue-red-emissive dyad, consisting of a rhodamine moiety responsive to acidic pH values and a pH-inert quinoline fluorophore, followed by the covalent attachment of a fluorescein dye to the particle surface that signals neutral and basic pH values with a green fluorescence. These sensor particles change their fluorescence from blue to red and green, depending on the pH and excitation wavelength, and enable ratiometric pH measurements in the pH range of 3.0−9.0. The localization of the different sensor dyes in the particle core and at the particle surface was confirmed with fluorescence microscopy utilizing analogously prepared polystyrene microparticles. To show the application potential of these polystyrene-based multicolor sensor particles, fluorescence microscopy studies with a human A549 cell line were performed, which revealed the cellular uptake of the pH nanosensor and the differently colored emissions in different cell organelles, that is, compartments of the endosomal-lysosomal pathway. Our results demonstrate the underexplored potential of biocompatible polystyrene particles for multicolor and multianalyte sensing and bioimaging utilizing hydrophobic and/or hydrophilic stimuli-responsive luminophores.
Ensemble and single particle studies of the excitation power density (P)-dependent upconversion luminescence (UCL) of core and core–shell β-NaYF4:Yb,Er upconversion nanoparticles (UCNPs) doped with 20% Yb3+ and 1% or 3% Er3+ performed over a P regime of 6 orders of magnitude reveal an increasing contribution of the emission from high energy Er3+ levels at P > 1 kW/cm2.
This changes the overall emission color from initially green over yellow to white. While initially the green and with increasing P the red emission dominate in ensemble measurements at P < 1 kW/cm2, the increasing population of higher Er3+ energy levels by multiphotonic processes at higher P in single particle studies results in a multitude of emission bands in the ultraviolet/visible/near infrared (UV/vis/NIR) accompanied by a decreased contribution of the red luminescence. Based upon a thorough analysis of the P-dependence of UCL, the emission bands activated at high P were grouped and assigned to 2–3, 3–4, and 4 photonic processes involving energy transfer (ET), excited-state absorption (ESA), cross-relaxation (CR), back energy transfer (BET), and non-radiative relaxation processes (nRP). This underlines the P-tunability of UCNP brightness and color and highlights the potential of P-dependent measurements for mechanistic studies required to manifest the population pathways of the different Er3+ levels.
pH presents one of the most important analytes in the life and material sciences, indicating, e.g., diseases and corrosion processes. This includes the optical monitoring of pH in living cells for studying cellular internalization pathways, such as phagocytosis, endocytosis, and receptor mediated internalization with the aid of molecular and nanoscale fluorescent sensors. Nanoparticle (NP)-based sensors, that are labelled or stained with a multitude of sensor dyes, have several advantages as compared to conventional molecular probes like enhanced brightness, i.e., amplified signals, ease of designing ratiometric systems by combining analyte-sensitive and inert reference dyes, and increased photostability. Moreover, this can enable the use of hydrophobic dyes in aqueous environments. Versatile templates and carriers for the fabrication of nanosensors by staining and/or labelling with different fluorophores and sensor molecules are surface-functionalized particles like silica (SiO2) and polystyrene (PS) particles. Here we present a platform of blue-red-green fluorescent pH nanosensors for the measurement of acidic, neutral, and basic pH utilizing both types of matrices and two spectrally distinguishable sensor dyes with an integrated reference dye and demonstrate its applicability for cellular studies.
Monodisperse iron oxide nanoparticles as reference material candidate for particle size measurements
(2020)
In order to utilize and rationally design materials at the nanoscale the reliable characterization of their physico-chemical properties is highly important, especially with respect to the assessment of their environmental or biological impact. Furthermore, the European Commission’s REACH Regulations require the registration of nanomaterials traded in quantities of at least 1 ton. Powders or dispersions where 50% (number distribution) of the constituent particles have sizes ≤ 100 nm in at least one dimension are defined as nanomaterials. This creates a need for industrial manufacturers and research or analytical service facilities to reliably characterize potential nanomaterials. Currently, BAM is developing reference nanoparticles, which shall expand the scarce list of worldwide available nano reference materials certified for particle size distribution and will also target other key parameters like shape, structure, porosity or functional properties. In this respect, materials like iron oxide or titanium dioxide are considered as candidates to complement the already available silica, Au, Ag, and polystyrene reference nanoparticles.
The thermal decomposition of iron oleate precursors in high boiling organic solvents can provide large quantities of iron oxide nanoparticles that can be varied in size and shape.[1, 2] The presence of oleic acid or other hydrophobic ligands as capping agents ensures stable dispersion in nonpolar solvents. Such monodisperse, spherical particles were synthesized at BAM and pre-characterized by electron microscopy (TEM, SEM including the transmission mode STEM-in-SEM) and dynamic light scattering comparing cumulants analysis and frequency power spectrum.
1. REACH regulations and nanosafety concerns create a strong need for nano reference materials with diverse properties.
2. Iron oxide nanoparticles are under development as new candidate reference material at BAM.
3. Narrow particle size distribution confirmed by light scattering and electron microscopy.
Biofilms are ubiquitous in nature and in the man-made environment. Given their harmful effects on human health, an in-depth understanding of biofilms and the monitoring of their formation and growth are important. Particularly relevant for many metabolic processes and survival strategies of biofilms is their extracellular pH. However, most conventional techniques are not suited for minimally invasive pH measurements of living biofilms. Here, a fluorescent nanosensor is presented for ratiometric measurements of pH in biofilms in the range of pH 4.5–9.5 using confocal laser scanning microscopy. The nanosensor consists of biocompatible polystyrene nanoparticles loaded with pH-inert dye Nile Red and is surface functionalized with a pH-responsive fluorescein dye. Its performance was validated by fluorometrically monitoring the time-dependent changes in pH in E. coli biofilms after glucose inoculation at 37 °C and 4 °C. This revealed a temperature-dependent decrease in pH over a 4-h period caused by the acidifying glucose metabolism of E. coli. These studies demonstrate the applicability of this nanosensor to characterize the chemical microenvironment in biofilms with fluorescence methods.
Photon upconversion upon 1550 nm excitation is of high relevance for applications in the third biological excitation window, for photovoltaics beyond current limitations, and enables appealing options in the field of glass Fiber telecommunications. Trivalent doped erbium ions (Er3+) are the material of choice for 1550 nm excited upconversion, however, they suffer from a low absorption cross-section and a low brightness. Therefore, the ability of Silicon metasurfaces to provide greatly enhanced electrical near-fields is employed to enable efficient photon upconversion even at low external Illumination conditions. Hexagonally shaped β-NaYF4:Er3+ nanoparticles are placed on large-area silicon metasurfaces designed to convert near-infrared (1550 nm) to visible light. More than 2400-fold enhanced photon upconversion luminescence is achieved by using this metasurface instead of a planar substrate.
With the aid of optical simulations based on the finite-element method, this result is attributed to the coupling of the excitation source with metasurface resonances at appropriate incident angles. Analysis of the excitation power density dependence of upconversion luminescence and red-to-green-emission ratios enables the estimation of nanoscale near-field enhancement on the metasurface. The findings permit the significant reduction of required external excitation intensities for photon upconversion of 1550 nm light, opening perspectives in biophotonics, telecommunication, and photovoltaics.
Large-scale nanoimprinted metasurfaces based on silicon photonic crystal slabs were produced and coated with a NaYF4:Yb3+/Er3+ upconversion nanoparticle (UCNP) layer. UCNPs on these metasurfaces yield a more than 500-fold enhanced upconversion emission compared to UCNPs on planar surfaces. It is also demonstrated how the optical response of the UCNPs can be used to estimate the local field energy in the coating layer. Optical simulations using the finite element method validate the experimental results and the calculated spatial three-dimensional field Energy distribution helps us to understand the emission enhancement mechanism of the UCNPs closely attached to the metasurface. In addition, we analyzed the spectral shifts of the resonances for uncoated and coated metasurfaces and metasurfaces submerged in water to enable a prediction of the optimum layer thicknesses for different excitation wavelengths, paving the way to applications such as electromagnetic field sensors or bioassays.
Lanthanide-based upconversion nanoparticles (UCNPs) like hexagonal 𝛽-NaYF4 UCNPs doped with Yb3+ and Er3+, which efficiently convert 976 nm light to ultraviolet, visible, and near infrared photons, offer new strategies for luminescence-based sensing, barcoding, and Imaging. Their upconversion (UC) luminescence (UCL) features like UCL intensity, quantum yield, relative spectral distribution / UCL luminescence color, and luminescence decay kinetics are, however, strongly influenced by particle size, dopant ion concentration, particle architecture, surface chemistry including presence and thickness of surface passivation and shielding shells, microenvironment/presence of quenchers with high energy vibrations, and excitation power density (P).
We present here a comprehensive study of the influence of excitation power density on the UCL features of different types of UCNPs, focusing on Yb3+ and Er3+ co-doped NaYF4 core-only and core-shell nanostructures with different sizes and doping ion concentration, which underlines the importance of P-dependent optimum dopant concentrations for UCNP performance and the potential of P-tuning of UCL.
Mandatory for the comparison of different emitter classes and the rational design of the next generation of molecular and nanoscale reporters are reliable and quantitative photoluminescence measurements. This is of special relevance for all fluorescence applications in the life and material sciences. In the following, procedures for the determination of this spectroscopic key parameter are presented including pitfalls and achievable uncertainties and material-specific effects related to certain emitter classes are addressed.
The efficient and sensitive detection of pathogenic microorganisms in aqueous environments, such as water used in medical applications, drinking water, and cooling water of industrial plants, requires simple and fast methods suitable for multiplexed detection such as flow cytometry (FCM) with optically encoded carrier beads. For this purpose, we combine fluorescent Cd-free Ag−In−S ternary quantum dots (t-QDs) with fluorescence Lifetimes (LTs) of several hundred nanoseconds and superparamagnetic Fe3O4 nanoparticles (SPIONs) with mesoporous CaCO3 microbeads to a magneto-fluorescent bead platform that can be surface-functionalized with bioligands, such as antibodies. This inorganic bead platform enables immuno-magnetic separation, target enrichment, and target quantification with optical readout. The beads can be detected with steady-state and time-resolved fluorescence microscopy and flow cytometry (FCM). Moreover, they are suited for readout by time gated emission. In the following, the preparation of these magneto-fluorescent CaCO3 beads, their spectroscopic and analytic characterization, and their conjugation with bacteria-specific antibodies are presented as well as proof-of-concept measurements with Legionella pneumophila including cell cultivation and plating experiments for bacteria quantification. Additionally, the possibility to discriminate between the long-lived emission of the LT-encoded capture and carrier CaCO3 beads and the short-lived Emission of the dye-stained bacteria with time-resolved fluorescence techniques and single wavelength excitation is demonstrated.
Fluorescent semiconductor nanocrystals, also known as quantum dots (QDs), enabled many advancements in biotechnology, photovoltaics, photocatalysis, quantum computing and display devices. The high versatility of this nanomaterial is based on their unique size-tunable photoluminescence properties, which can be adjusted from the visible to the near-infrared range. In contrast to other nanomaterials, QDs made the transition from a laboratory curiosity to the utilization in commercial products, like the QLED television screen or in smartphone displays. The best investigated QDs are composed of heavy metals like cadmium or lead, which is not the best choice in terms of toxicity and environmental pollution. A more promising material is Indium Phosphide (InP), which is also currently used by Samsung, Sony and co. in the QLED displays.
In this contribution, I would like to give you a sneak peek behind the curtains of nanomaterial synthesis and show how this material is produced, how to stabilize their structural properties, and assess their toxicity in environmentally relevant conditions. Furthermore, I would like to present a synthesis method to accomplish the last open challenge in display technology of a blue luminescent LED based on QDs by introducing a new element to the InP QDs.
Inorganic nanocrystals with linear and nonlinear luminescence in the ultraviolet, visible, near infrared and short-wave infrared like semiconductor quantum dots and spectrally shifting lanthanide-based nanophosphors have meanwhile found many applications in the life and material sciences. This includes optical reporters for bioimaging and sensing, security and authentication barcodes, solid state lighting, converter materials, and photovoltaics. The identification of optimum particle structures requires quantitative spectroscopic studies under application-relevant conditions, focusing on the key performance parameter photoluminescence quantum yield, ideally flanked by single particle studies to assess spectroscopic inhomogeneities on a particle-to-particle level for typical preparation methods. In this context, methods to quantify the photoluminescence of these different nanoscale emitters are shown and utilized as a basis for a profound mechanistic understanding of the nonradiative deactivation pathways in semiconductor and upconversion nanocrystals of different size and particle architecture in different environments. Exemplary for the application potential of such nanomaterials, in addition, the design of optical sensors from different nanomaterials and functional organic dyes is briefly summarized.
Bioanalytical, diagnostic, and security applications require the fast and sensitive determination of a steadily increasing number of analytes or events in parallel in a broad variety of detection formats.[1,2] Ideal candidates for spectral encoding and multiplexing schemes are luminescent nanocrystals like semiconductor quantum dots (QDs), particularly Cd-containing II/VI QDs with their narrow and symmetric emission bands. With the availability of relatively simple and inexpensive instrumentation for time-resolved fluorescence measurements, similar strategies utilizing the compound-specific parameter fluorescence lifetime or fluorescence decay kinetics become increasingly attractive.[3-5] The potential of different types of QDs like II/VI, III/V and Cd-free ternary QDs such as AgInS (AIS) QDs for lifetime-based encoding and multiplexing has been, however, barely utilized, although the lifetimes of these nanocrystals cover a time windows which is barely accessible with other fluorophores. Here we present a brief insight into the photophysics of AIS QDs and show the potential of dye- and QD-encoded beads for lifetime-based encoding and detection schemes in conjunction with flow cytometry and fluorescence lifetime imaging microscopy
Different types of optical spectroscopies are introduced with special emphasis on method-inherent limitations and reliable instrument calibration and performance validation. In addition, procedures for the determination of spectroscopic key parameters like the photoluminescence quantum yield are presented including required instrument calibrations and material-specific effects related to certain emitters.