Ingenieurwissenschaften und zugeordnete Tätigkeiten
Filtern
Erscheinungsjahr
Dokumenttyp
- Zeitschriftenartikel (125)
- Vortrag (61)
- Beitrag zu einem Tagungsband (5)
- Posterpräsentation (3)
- Sonstiges (2)
- Buchkapitel (1)
- Corrigendum (1)
Schlagworte
- Quantum yield (97)
- Fluorescence (88)
- Nano (56)
- NIR (54)
- Lifetime (53)
- Dye (48)
- Nanoparticle (48)
- Photophysics (45)
- Quality assurance (44)
- Sensor (41)
Organisationseinheit der BAM
- 1 Analytische Chemie; Referenzmaterialien (151)
- 1.2 Biophotonik (151)
- 6 Materialchemie (14)
- 6.1 Oberflächen- und Dünnschichtanalyse (11)
- 6.3 Strukturanalytik (4)
- 1.0 Abteilungsleitung und andere (3)
- 1.7 Organische Spuren- und Lebensmittelanalytik (3)
- 5 Werkstofftechnik (3)
- 7 Bauwerkssicherheit (3)
- 4 Material und Umwelt (2)
Paper des Monats
- ja (5)
Eingeladener Vortrag
- nein (61)
High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid
NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%‒98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%‒40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ~9% and ~25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ~9% (20% Yb3+) to ~7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ~7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials.
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.
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.
Asymmetrically bridged aroyl-S,N-ketene acetals and aroyl-S,N-ketene acetal multichromophores can be readily synthesized in consecutive three-, four-, or five-component syntheses in good to excellent yields by several successive Suzuki-couplings of aroyl-S,N-ketene acetals and bis(boronic)acid esters. Different aroyl-S,N-ketene acetals as well as linker molecules yield a library of 23 multichromophores with substitution and linker pattern-tunable emission properties. This allows control of different communication pathways between the chromophores and of aggregation-induced emission (AIE) and energy transfer (ET) properties, providing elaborate aggregation-based fluorescence switches.
Anear-infrared (NIR) light-triggered release method for nitric oxide (NO) was developed utilizing core/shell NaYF4: Tm/Yb/Ca@NaGdF4:Nd/Yb up-conversion nanoparticles (UCNPs) bearing a mesoporous silica (mSiO2) shell loaded with theNOdonor S-nitroso-N-acetyl-DL-penicillamine (SNAP). To avoid overheating in biological samples, Nd3+ was chosen as a sensitizer, Yb3+ ions as the bridging sensitizer, andTm3+ ions as UV-emissive activator while co-doping with Ca2+ was done to enhance the luminescence of the activatorTm3+.NOrelease from SNAP was triggered by an NIR-UV up-conversion process, initiated by 808nmlight absorbed by the Nd3+ ions.NOrelease was confirmed by the Griess method. Under 808nmirradiation, the viability of the liver cancer cell line HepG2 significantly decreased with increasing UCNPs@mSiO2-SNAP concentration. For a UCNPs@mSiO2-SNAP concentration of 200 μgml−1, the cell survival probability was 47%. These results demonstrate that UCNPs@mSiO2-SNAP can induce the release of apoptosis-inducingNOby NIR irradiation.
Core–shell nanoparticles have attracted much attention in recent years due to their unique properties and their increasing importance in many technological and consumer products. However, the chemistry of nanoparticles is still rarely investigated in comparison to their size and morphology. In this review, the possibilities, limits, and challenges of X-ray photoelectron spectroscopy (XPS) for obtaining more insights into the composition, thickness, and homogeneity of nanoparticle coatings are discussed with four examples: CdSe/CdS quantum dots with a thick coating and a small core; NaYF4-based upconverting nanoparticles with a large Yb-doped core and a thin Er-doped coating; and two types of polymer nanoparticles with a poly(tetrafluoroethylene) core with either a poly(methyl methacrylate) or polystyrene coating. Different approaches for calculating the thickness of the coating are presented, like a simple numerical modelling or a more complex simulation of the photoelectron peaks. Additionally, modelling of the XPS background for the investigation of coating is discussed. Furthermore, the new possibilities to measure with varying excitation energies or with hard-energy X-ray sources (hard-energy X-ray photoelectron spectroscopy) are described. A discussion about the sources of uncertainty for the determination of the thickness of the coating completes this review.
Light-emitting nanoparticles like semiconductor nanocrystals (termed quantum dots, QDs) are promising candidates for biosensing and bioimaging applications based on their bright and stable photoluminescent properties. As high-quality QDs are often synthesized in organic solvents, strategies needed to be developed to render them water-dispersible without affecting their optical properties and prevent changes in postmodification steps like the biofunctionalization with antibodies or DNA. Despite a large number of studies on suitable surface modification procedures, the preparation of water-soluble QDs for nanobiotechnology applications still presents a challenge. To highlight the advantages of surface silanization, we systematically explored the influence of the core/multishell architecture of CdSe/CdS/ZnS QDs and the silanization conditions on the optical properties of the resulting silanized QDs. Our results show that the optical properties of silica-coated CdSe/CdS/ZnS QDs are best preserved in the presence of a thick CdS (6 monolayers (ML)) intermediate shell, providing a high photoluminescence quantum yield (PL QY), and a relatively thick ZnS (4.5 ML) external shell, effectively shielding the QDs from the chemical changes during silica coating. In addition to the QD core/shell architecture, other critical parameters of the silica-coating process, that can have an influence on the optical properties of the QD, include the choice of the surfactant and its concentration used for silica coating. The highest PL QY of about 46% was obtained by a microemulsion silica-coating procedure with the surfactant Brij L4, making these water-dispersible QDs to wellsuited optical reporters in future applications like fluorescence immunoassays, biomedicine, and bioimaging.
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.
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.
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.
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.
Imaging in the shortwave-infrared region (SWIR, λ = 1000–2500 nm) has the potential to enable deep tissue imaging with high resolution. Critical to the development of these Methods is the identification of low molecular weight, biologically compatible fluorescent probes that emit beyond 1000 nm.
Exchanging the bridging oxygen atom on the xanthene scaffold (C10’ position) with electron withdrawing groups has been shown to lead to significant redshifts in absorbance and emission. Guided by quantum chemistry computational modeling studies, we investigated the installation of a Ketone bridge at the C10’ position. This simple modification extends the absorbance maxima to 860 nm and the emission beyond 1000 nm, albeit with reduced photon output. Overall, These studies demonstrate that broadly applied xanthene dyes can be extended into the SWIR range.
Risk assessment of nanomaterials requires not only standardized toxicity studies but also validated methods for nanomaterial surface characterization with known uncertainties. In this context, a first bilateral interlaboratory comparison on Surface group quantification of nanomaterials is presented that assesses different reporter-free and labeling methods for the quantification of the total and accessible number of amine functionalities on commercially available silica nanoparticles that are widely used in the life sciences. The overall goal of this comparison is the identification of optimum methods as well as achievable measurement uncertainties and the comparability of the results across laboratories. We also examined the robustness and ease of implementation of the applied analytical methods and discussed method-inherent limitations. In summary, this comparison presents a first step toward the eventually required standardization of methods for surface group quantification.
Enhanced photon upconversion using erbium-doped nanoparticles interacting with silicon metasurfaces
(2021)
Photon upconversion (UC) using trivalent erbium (Er+3) doped crystals is a promising concept to harness near infrared photons of the solar spectrum which cannot be directly absorbed by silicon solar cells. However, their UC efficiency at low-intensity 1 sun illumination is not relevant on device level so far. Exploiting giant near-field enhancement effects on metasurfaces is an appealing approach to enable efficient UC at low irradiance conditions. Here, we report on more than 1000-fold enhanced photon UC of NaYF4:Er+3 nanoparticles interacting with the near-fields supported by a silicon metasurface under 1550 nm excitation.
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.
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.
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.
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.
Despite considerable advances in synthesizing high-quality core/shell upconversion (UC) nanocrystals (NC; UCNC) and UCNC photophysics, the application of near-infrared (NIR)-excitable lanthanide-doped UCNC in the life and material sciences is still hampered by the relatively low upconversion luminescence (UCL) of UCNC of small size or thin protecting shell. To obtain deeper insights into energy transfer and surface quenching processes involving Yb3+ and Er3+ ions, we examined energy loss processes in differently sized solid core NaYF4 nanocrystals doped with either Yb3+ (YbNC; 20% Yb3+) or Er3+ (ErNC; 2% Er3+) and co-doped with Yb3+ and Er3+ (YbErNC; 20% Yb3+ and 2% Er3+) without a surface protection shell and coated with a thin and a thick NaYF4 shell in comparison to single and co-doped bulk materials. Luminescence studies at 375 nm excitation demonstrate backenergy transfer (BET) from the 4G11/2 state of Er3+ to the 2F5/2 state of Yb3+, through which the red Er3+ 4F9/2 state is efficiently populated. Excitation power density (P)-dependent steady state and time-resolved photoluminescence measurements at different excitation and emission wavelengths enable to separate surface-related and volume-related effects for two-photonic and threephotonic processes involved in UCL and indicate a different influence of surface passivation on the green and red Er3+ emission.
The intensity and lifetime of the latter respond particularly to an increase in volume of the active UCNC core. We provide a threedimensional random walk model to describe these effects that can be used in the future to predict the UCL behavior of UCNC.
Functional nanomaterials (NM) of different size, shape, chemical composition, and surface chemistry are of increasing relevance for many key technologies of the twenty-first century. This includes polymer and silica or silica-coated nanoparticles (NP) with covalently bound surface groups, semiconductor quantum dots (QD), metal and metal oxide NP, and lanthanide-based NP with coordinatively or electrostatically bound ligands, as well as surface-coated nanostructures like micellar encapsulated NP. The surface chemistry can significantly affect the physicochemical properties of NM, their charge, their processability and performance, as well as their impact on human health and the environment. Thus, analytical methods for the characterization of NM surface chemistry regarding chemical identification, quantification, and accessibility of functional groups (FG) and surface ligands bearing such FG are of increasing importance for quality control of NM synthesis up to nanosafety. Here, we provide an overview of analytical methods for FG analysis and quantification with special emphasis on bioanalytically relevant FG broadly utilized for the covalent attachment of biomolecules like proteins, peptides, and oligonucleotides and address methodand material-related challenges and limitations. Analytical techniques reviewed include electrochemical titration methods, optical assays, nuclear magnetic resonance and vibrational spectroscopy, as well as X-ray based and thermal analysis methods, covering the last 5–10 years. Criteria for method classification and evaluation include the need for a signal-generating label, provision of either the total or derivatizable number of FG, need for expensive instrumentation, and suitability for process and production control during NM synthesis and functionalization.
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.
The concept of aggregation-induced emission represents a means to rationalise photoluminescence of usually nonfluorescent excimers in solid-state materials. In this publication, we study the photophysical properties of selected diaminodicyanoquinone (DADQ) derivatives in the solid state using a combined approach of experiment and theory. DADQs are a class of high-dipole organic chromophores promising for applications in non-linear optics and light-harvesting devices. Among the compounds investigated, we find both aggregation-induced emission and aggregation-caused quenching effects rationalised by calculated energy transfer rates. Analysis of fluorescence spectra and lifetime measurements provide the interesting result that (at least) two emissive species seem to contribute to the photophysical properties of DADQs. The main emission peak is notably broadened in the long-wavelength limit and exhibits a blue-shifted shoulder. We employ high-level quantum-chemical methods to validate a molecular approach to a solid-state problem and show that the complex emission features of DADQs can be attributed to a combination of H-type aggregates, monomers, and crystal structure defects.
Aroyl-S,N-ketene acetal-based bichromophores can be readily synthesized in a consecutive three-component synthesis in good to excellent yields by condensation of aroyl chlorides and an N-(p-bromobenzyl) 2-methyl benzothiazolium salt followed by a Suzuki coupling, yielding a library of 31 bichromophoric fluorophores with substitution patterntunable emission properties. Varying both chromophores enables different communication pathways between the chromophores, exploiting aggregation-induced emission (AIE) and energy transfer (ET) properties, and thus, furnishing aggregation-based fluorescence switches. Possible applications range from fluorometric analysis of alcoholic beverages to pH sensors.
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.
Luminescent solar concentrators (LSC) allow to obtain renewable energy from building integrated photovoltaic systems. As promising efficient and long-term stable LSC fluorophores semiconductor nanocrystals like Quantum dots (QDs) with size and composition tunable optoelectronic properties have recently emerged. The most popular II/VI or IV/VI semiconductor QDs contain, however, potentially hazardous cadmium or lead ions, which is a bottleneck for commercial applications. A simple aqueous based, microwaveassisted synthesis for environmentally friendly and highly emissive AgInS2/ ZnS QDs is developed using 3-mercaptopropionic acid (MPA) and glutathione (GSH) and their incorporation into polylaurylmethacrylate (PLMA) polymer slabs integrable in LSC devices (10.4 × 10.4 × 0.2 cm3, G = 12.98).
With this simple approach, optical power efficiencies (OPE) of 3.8% and 3.6% and optical quantum efficiencies (OQE) of 24.1% and 27.4% are obtained, which are among the highest values yet reported.
The publicly available document encapsulates the first version of the Catalogue of Services of the future EC4Safenano Centre (CoS 2019).
The CoS 2019 is structured in 12 Service Categories and 27 Service Topics, for each of the 12 categories considered. This architecture configures a 12 x 27 matrix that allows ordering the potential EC4Safenano offer in 324 types of services/groups of services.
Each type of service/group of services is described, in a simple and friendly way, by means of a specific service sheet: the EC4Safenano - Service Data Sheet (EC4-SDS). These EC4-SDSs allow structuring and summarizing the information of each service, providing the customer with a concise view of characteristics of the service and also the contact details with the service provider.
The CoS 2019 deploys a map of services consisting of a set of 100 EC4-SDSs, covering 7 of the 12 Service Categories and 17 of the 27 Service Topics.
The harmonization of services is visualized as a future necessary step in EC4Safenano, in order to strengthen the offer and provide added value to customers with a growing offer of harmonized services in future versions of the CoS.
The information contained in this document is structured in 3 main sections, as follows:
• Catalogue structure. This section describes in short the main characteristics of the CoS 2019.
• Catalogue content. This section represents the core part of the document and encapsulates the set of 100 SDSs displaying the offer proposed by the CoS 2019.
• Online Catalogue. This section describes the resources implemented by EC4Safenano to facilitate the on-line consultation of the CoS 2019 by customers and other interested parties.
Molecular aggregation alters the optical properties of a system as fluorescence may be activated or quenched. This is usually described within the well-established framework of H- and J-aggregates. While H-aggregates show nonfluorescent blueshifted absorption bands with respect to the isolated monomer, Jaggregates are fluorescent displaying a redshifted peak. In this publication, we employ a combined approach of experiment and theory to study the complex aggregation features and photophysical properties of diaminodicyanoquinone derivatives, which show unusual and puzzling nonfluorescent redshifted Absorption bands upon aggregation. Our theoretical analysis demonstrates that stable aggregates do not account for the experimental observations.
Instead, we propose an unprecedented mechanism involving metastable dimeric species formed from stable dimers to generate nonfluorescent J-aggregates. These results represent a novel kind of aggregation-induced optical effect and may have Broad implications for the photophysics of dye aggregates.
In this work, we describe the synthesis, structural and photophysical characterization of four novel Pd(II) and Pt(II) complexes bearing tetradentate luminophoric ligands with high photoluminescence quantum yields (FL) and long excited state lifetimes (s) at room temperature, where the results were interpreted by means of DFT calculations. Incorporation of fluorine atoms into the tetradentate ligand favors aggregation and thereby, a shortened average distance between the metal centers, which provides accessibility to metal–metal-to-ligand charge-transfer (3MMLCT) excimers acting as red-shifted Energy traps if compared with the monomeric entities. This supramolecular approach provides an elegant way to enable room-temperature phosphorescence from Pd(II) complexes, which are otherwise quenched by a thermal population of dissociative states due to a lower ligand field splitting. Encapsulation of These complexes in 100 nm-sized aminated polystyrene nanoparticles enables concentration-controlled aggregation-enhanced dual emission. This phenomenon facilitates the tunability of the absorption and emission colors while providing a rigidified environment supporting an enhanced FL up to about 80% and extended s exceeding 100 ms. Additionally, these nanoarrays constitute rare examples for selfreferenced oxygen reporters, since the phosphorescence of the aggregates is insensitive to external influences, whereas the monomeric species drop in luminescence lifetime and intensity with increasing triplet molecular dioxygen concentrations (diffusion-controlled quenching).
The use of inorganic lanthanide-doped upconversion nanoparticles (UCNP) in bioimaging and cellular studies requires biocompatible particles. One possible cause of UCNP toxicity is the release of potentially harmful fluoride and lanthanide ions as revealed by dilution studies in aqueous environments, particularly under high dilution conditions. To address this issue, suitable surface coatings preventing such effects in combination with fast screening methods suited for online monitoring and in situ analyses are desired.
Here we present systematic studies of differently sized β-NaYF4:Yb,Er UCNP stabilized with different surface coatings and hydrophilic ligands varying in binding strength to the particle surface in various aqueous environments at different temperatures and UCNP concentrations. The concentration of the fluoride and lanthanide ions released upon particle dissolution was quantified electrochemically with a fluoride ion-sensitive electrode and inductively coupled plasma optical emission spectrometry (ICP-OES) and monitored fluorometrically, thereby exploiting the sensitivity of the upconversion luminescence to changes in size and surface chemistry. Moreover, changes in surface chemistry were determined with X-Ray photoelectron spectroscopy (XPS). Based upon our results, we could derive optimum screening parameters for UCNP stability studies and determine conditions and coating procedures and ligands for enhancing UCNP stability in aqueous environments.
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.
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 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.
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.
Controlling thickness and tightness of surface passivation shells is crucial for many applications of core–shell nanoparticles (NP). Usually, to determine shell thickness, core and core/shell particle are measured individually requiring the availability of both nanoobjects. This is often not fulfilled for functional nanomaterials such as many photoluminescent semiconductor quantum dots (QD) used for bioimaging, solid state lighting, and display technologies as the core does not show the applicationrelevant functionality like a high photoluminescence (PL) quantum yield, calling for a whole nanoobject approach. By combining high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS), a novel whole nanoobject approach is developed representatively for an ultrabright oleic acid-stabilized, thick shell CdSe/CdS QD with a PL quantum yield close to unity. The size of this spectroscopically assessed QD, is in the range of the information depth of usual laboratory XPS. Information on particle size and monodispersity were validated with dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) and compared to data derived from optical measurements. In addition to demonstrating the potential of this novel whole nanoobject approach for determining architectures of small nanoparticles, the presented results also highlight challenges faced by different sizing and structural analysis methods and method-inherent uncertainties.
Between Aromatic and Quinoid Structure: A Symmetrical UV to Vis/NIR Benzothiadiazole Redox Switch
(2020)
Reversibly switching the light absorption of organic molecules by redox processes is of interest for applications in sensors, light harvesting, smart materials, and medical diagnostics. This work presents a symmetrical benzothiadiazole (BTD) derivative with a high fluorescence quantum yield in solution and in the crystalline state and shows by spectroelectrochemical analysis that reversible switching of UV absorption in the neutral state, to broadband Vis/NIR absorption in the 1st oxidized state, to sharp band Vis absorption in the 2nd oxidized state, is possible.
For the one-electron oxidized species, formation of a delocalized radical is confirmed by electron paramagnetic resonance spectroelectrochemistry. Furthermore, our results reveal an increasing quinoidal distortion upon the 1st and 2nd oxidation, which can be used as the leitmotif for the development of BTD based redox switches.
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.
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.
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 brief introduction to fluorescence spectroscopy will be provided, ranging from typically measured fluorescence quantities over instrument-specific contributions to measured fluorescence signals to selected applications. In this context, an overview of the photoluminescence properties of molecular and nanoscale luminescence reporters will be given including a brief insight into their photophysics and fluorescence standards designed by division Biophotonics for the calibration and instrument performance validation of fluorescence measuring devices will be presented.
A brief introduction to fluorescence spectroscopy will be provided, ranging from typically measured fluorescence quantities over instrument-specific contributions to measured fluorescence signals to selected applications. In this context, an overview of the photoluminescence properties of molecular and nanoscale luminescence reporters will be given including a brief insight into their photophysics and fluorescence standards designed by division Biophotonics for the calibration and instrument performance validation of fluorescence measuring devices will be presented.
To demonstrate the potential of time-resolved flow cytometry (FCM) for bioanalysis, clinical diagnostics, and optically encoded bead-based assays, we performed a proof-of-principle study to detect biomolecular interactions utilizing fluorescence lifetime (LT)-encoded micron-sized polymer beads bearing target-specific bioligands and a recently developed prototype lifetime flow cytometer (LT-FCM setup). This instrument is equipped with a single excitation light source and different fluorescence detectors, one operated in the photon-counting mode for time-resolved measurements of fluorescence decays and three detectors for conventional intensity measurements in different spectral windows. First, discrimination of bead-bound biomolecules was demonstrated in the time domain exemplarily for two targets, Streptavidin (SAv) and the tumor marker human chorionic gonadotropin (HCG). In a second step, the determination of biomolecule concentration levels was addressed representatively for the inflammation-related biomarker tumor necrosis factor (TNF-α) utilizing fluorescence intensity measurements in a second channel of the LT-FCM instrument. Our results underline the applicability of LT-FCM in the time domain for measurements of biomolecular interactions in suspension assays. In the future, the combination of spectral and LT encoding and multiplexing and the expansion of the time scale from the lower nanosecond range to the longer nanosecond and the microsecond region is expected to provide many distinguishable codes. This enables an increasing degree of multiplexing which could be attractive for high throughput screening applications.
We studied the dissolution behavior of β NaYF4:Yb(20%), Er(2%) UCNP of two different sizes in biologically relevant media i.e., water (neutral pH), phosphate buffered saline (PBS), and Dulbecco’s modified Eagle medium (DMEM) at different temperatures and particle concentrations. Special emphasis was dedicated to assess the influence of different surface functionalizations, particularly the potential of mesoporous and microporous silica shells of different thicknesses for UCNP stabilization and protection. Dissolution was quantified electrochemically using a fluoride ion selective electrode (ISE) and by inductively coupled plasma optical emission spectrometry (ICP OES). In addition, dissolution was monitored fluorometrically. These experiments revealed that a thick microporous silica shell drastically decreased dissolution. Our results also underline the critical influence of the chemical composition of the aqueous environment on UCNP dissolution. In DMEM, we observed the formation of a layer of adsorbed molecules on the UCNP surface that protected the UCNP from dissolution and enhanced their fluorescence. Examination of this layer by X ray photoelectron spectroscopy (XPS) and mass spectrometry (MS) suggested that mainly phenylalanine, lysine, and glucose are adsorbed from DMEM. These findings should be considered in the future for cellular toxicity studies with UCNP and other nanoparticles and the design of new biocompatible surface coatings.
We developed a procedure to prepare luminescent LiYF4:Yb/LiYF4 and LiYF4:Yb,Er/LiYF4 core/shell nanocrystals with a size of approximately 40 nm revealing luminescence decay times of the dopant ions that approach those of high-quality laser crystals of LiYF4:Yb (Yb:YLF) and LiYF4:Yb,Er (Yb,Er:YLF) with identical doping concentrations. As the luminescence decay times of Yb3+ and Er3+ are known to be very sensitive to the presence of quenchers, the long decay times of the core/shell nanocrystals indicate a very low number of defects in the core particles and at the core/shell interfaces. This improvement in the performance was achieved by introducing two important modifications in the commonly used oleic acid based synthesis. First, the shell was prepared via anewly developed method characterized by a very low nucleation rate for particles of pure LiYF4 shell material. Second, anhydrous acetates were used as precursors and additional drying steps were applied to reduce the incorporation of OH− in the crystal lattice, known to quench the emission of Yb3+ ions. Excitation power density (P)-dependent absolute measurements of the upconversion luminescence quantum yield (Φ,UC) of LiYF4:Yb,Er/LiYF4 core/shell particles reveal a maximum value of 1.25% at P of 180 W·cm−2.
Although lower than the values reported for NaYF4:18%Yb,2%Er core/shell nanocrystals with comparable sizes, these Φ, UC values are the highest reported so far for LiYF4:18%Yb,2%Er/LiYF4 nanocrystals without additional dopants. Further improvements May nevertheless be possible by optimizing the dopant concentrations in the LiYF4 nanocrystals.
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.
Light-induced NO release based on exogenous NO donors has attracted substantial attention in clinical applications; the induction light source usually converts near-infrared light to blue or ultraviolet light.
However, the low efficiency of near-infrared light-assisted chemical light energy conversion remains a challenge, especially for NaYF4:Yb3+/Tm3+ photoconverting near-infrared light to ultraviolet (UV) and blue light. In this paper, a luminescence-enhanced strategy is reported by doping Ca2+ into NaYF4:Yb3+/Tm3+ and coating it with NaGdF4 through a two-step solvothermal method. Then, UCNPs modified with methyl-b-cyclodextrin (M-b-CD) are loaded on a ruthenium nitrosyl complex [(3)Ru(NO)(Cl)] as nitric oxide release-molecules (NORMs). X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) data demonstrated that Ca2+ was successfully doped into NaYF4:Yb3+/Tm3+ nanoparticles as the core, and a pure hexagonal phase, NaYF4, was obtained from the doping of Ca2+. TEM revealed that the crystallinity was significantly improved after Ca2+ doping, and the core–shell structure was successfully synthesized, with NaGdF4 directionally grown on the NaYF4:Ca/Yb/Tm core. Fluorescence tests showed that, especially in the ultraviolet and blue light excitation wavelength regions, the UC emission intensity of the Ca-doped NaYF4:Yb3+/Tm3+@NaGdF4 core–shell UCNPs increased by 302.95 times vs. NaYF4:Yb3+/Tm3+ UCNPs. Finally, the release of NO was tested by the Griess method. Under 980 nm irradiation, the cell viability distinctly decreased with increasing UCNPs@M-b-CD-NORMs concentration. This study Shows that NORM release of NO is triggered by enhanced up-converted UV and blue light, which can be used for the development of UV photo-sensitive drugs.
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.
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.
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.