Analytische Chemie
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Lanthanide-doped photon-upconversion nanoparticles (UCNPs) have been in the focus of many research activities in the material and life sciences over the last 15 years because of their potential to convert light between different spectral regions and their unique photophysical properties. In order to fully exploit the application potential of these fascinating nanomaterials, a number of challenges has to be overcome such as the low brightness particularly of small UCNPs and the reliable quantification of the excitation power density (P)-dependent upconversion luminescence (UCL). Here, the need and requirements on the characterization of the optical properties of UCNPs are discussed with special focus on the reliabiliy and comparability of relative and quantitative luminescence measurements and prerequisites for their standardization.
Ternary semiconductors Quantum Dots (t-QDs) like AgInS (AIS) QDs are interesting alternatives to Cd-based QDs for applications as optical active materials in light-emitting diodes (LEDs), solar concentrators and solar cells as well as as biodiagnostic tools, respectively.
AIS QDs exhibit broad photoluminescence (PL) spectra in the visible and near infrared, which are tunable by size and chemical composition (ratio of components or doping).
In order to enhance the PL quantum yield (PL QY or Fpl) and prevent material deterioration and oxidation, these QDs are covered by ZnS shell. Here we show a spectroscopic study of differently colored AIS QDs synthesized in water, evaluating their PL properties, their PL QY and their PL decay.
The simple aqueous synthesis that avoids further ligand exchange steps for bioanalytical applications, the tunable emission color, the high PL QY, the high absorption coefficients and the long lifetime make these t-QDs promising Cd-free materials as biodiagnostic tools or optical active materials.
Nanoparticles (NPs) have potential applications in medical diagnostics, imaging, drug delivery and other kinds of therapy. Furthermore, studies concerning nanoparticle uptake by cells are important for risk assessment. Size, shape and surface modification of the NPs determine the uptake rate and pathway into the cells, and therefore impact specific cell components and processes. Understanding the different uptake mechanisms and involved processes require sub-cellular resolution to determine, for example, whether the nanoparticles are reaching the nucleus. Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) is an established quantitative multi-elemental analysis and mapping technique. However, sub-cellular imaging has traditionally been challenging to achieve due to a lack of sensitivity at small laser spots. But now novel laser ablation systems with improved sensitivity and washout time allow imaging at high lateral resolution with spot sizes down to 1 µm.
Here LA-ICP-MS was applied for the imaging of individual fibroblast cells to study the uptake and intracellular processing of metal-containing NPs. To indicate cell morphology the local distribution of naturally occurring elements in cells like P and Zn was measured, too. Our results show that LA-ICP-MS can be used to localise nanoparticle aggregates within cellular compartments. The studied NPs accumulate in the perinuclear region in the course of intracellular processing, but do not enter the cell nucleus. The uptake efficiency depends strongly on the physico-chemical properties of the nanostructures as well as on the incubation conditions like concentration and incubation time. The potential of LA-ICP-MS for analysis at single cell level will be demonstrated.
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 flourescence entensities. 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 designg of new flourophores with improved properties.
Here, we present strategies to versatile method-adaptable liquid and solid flourescence Standards for different flourescence paramters including traceable Instrument calibration procedures and the design of integrating spere setups for the absolute measurements of emission spectra and Quantum yields in the wavelength Region of 350 to 1600 nm. Examples are multi-Emitter glasses, spectral flourescence Standards, and quantum yield Standards for the UV/vis/NIR.
At the core of luminescence color and lifetime Tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the Impact of the particle architecture for commonly used sensitizer (S) and activator (A) Ions. In this respect, a series of core@Shell NaYF4 UCNPs doped with Yb3+ and Ho3+ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@..., ...@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core-Shell NPs. As refealed by quantitative steady-state and time-resolved luminescence studies, the relative spatial Distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical Impact on ther luminescence characteristics. Although the increased amount of Yb3+ Ions boosts UCNP Performance by amplifying the Absorption, the Yb3+ ions can also efficiently dissipate the energy stored in the material through energy Migration to the surface, thereby reducing the Overall energy Transfer Efficiency to the activator ions. The results provide yet another proof that UC Phosphor chemistry combined with materials Engineering through intentional core@shell structures may help to fine-tune the luminescence Features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and Display technologies.
Semiconductor nanocrystals with a spherical (QDs) core and a spherical or a rod-shaped Shell, u.a., so-called Quantum dot-Quantum rods (QDQRs) are increasingly used as fluorescent Reporters or optically active components in the life and material science, e.g., in solid state lightening including Plasma Displays. (1,2) Morever, there is an increasing interest in materials with emission >800 nm for bioanalysis, medical diagnostics, and safety barcodes. Prerequisites for the mechanistic understanding of nonradiativ decay channels needed for the rational design of improved nanomaterials and the comparison of material Performance are reliable fluorescence measurements and validated methods for the assessment of their surface chemistry. (3,4) The latter is of particular importance for nanocrystalline Emitters, where surface states and the accessibility of emissive states by quenchers largely control photoluminescence properties. (5) Here, we present results from systematic spectroscopic studies including absolutely measured photolumunescence Quantum yields of different vissible and NIR emisisve QD and QDQRs Systems of varying particle architecture size and surface chemistries in Dispersion and embedded in salt crystals. (6,7)
The rational design of functional nanomaterials for optical applications in the material and life sciences requires optical-spectroscopic methods for the quantitative characterization of their signal-relevant optical properties. Additionally, methods for the simple and quantitative analysis of the surface chemistry are desired as the chemical nature and number of the surface groups and ligands can affect the optical features and controls the interaction of these nanomaterials with their environment. Here, we present quantitative photoluminescenvce studies of different types of vis/NIR-emissive nanomaterials like semiconductor quantum dots and upconversion nanocrystals will be presented and their relevance for the mechanistic understanding of nonradiative decay channels and the rational design of new nanomaterials will be underpinned. In this respect, also validation concepts for such measurements and absolute fluorometry will be introduced. In addition, the potential of optical spectroscopy for surface group and ligand analysis surface chemistry will be demonstrated exemplarily for semiconductor quantum dots
At the core of luminescence color and lifetime tuning of rare earth doped upconverting nanoparticles (UCNPs) is the understanding of the impact of the particle architecture for commonly used sensitizer (S) and activator (A) ions. In this respect, we present here a series of core@shell NaYF4 UCNPs doped with Yb3+ and Ho3+ ions, where the same dopant concentrations were distributed in different particle architectures following the scheme: YbHo core and YbHo@..., …@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core-shell NPs. As revealed by quantitative steady state and time-resolved luminescence studies, the relative spatial distribution of the A and S ions in the UCNPs and their protection from surface quenching has critical impact on their luminescent characteristics. Interestingly, although the increased amount of Yb3+ ions boosts UCNP performance by increasing the absorption, the Yb3+ ions can also dissipate the energy stored in the material through energy migration to surface, thereby reducing the overall energy transfer efficiency to the activator ions.
Polymer nanoparticles (NPs) are of increasing importance for a wide range of applications in the material and life sciences. This includes their use as carriers for dye molecules and drugs, multichromophoric reporters for signal enhancement strategies in optical assays, targeted probes in bioimaging studies, and nanosensors.[1] Application-relevant properties of such NPs include their size, morphology, colloidal stability, and ease of surface functionalization with e.g., sensor molecules and targeting ligands. Many of these features as well as the interaction of NPs with their microenvironment are closely linked to the knowledge of the chemical nature and total number of surface groups as well as the number of surface functionalities accessible for subsequent coupling reactions of differently sized ligands, biomolecules or reporter molecules. This underlines the importance of simple, robust, reliable, and validated methods, which can be employed for the characterization of a broad variety of particle systems independent of their optical properties, i.e., scattering or the presence of encoding dyes.[2]
In this respect, we assessed a variety of conventional and newly developed colorimetric or fluorometric labels for the optical surface group analysis, utilizing e.g., changes in intensity and/or color for signal generation.[3] Moreover, novel cleavable and multimodal reporters were developed which consist of a reactive group, a cleavable linker, and an optically active moiety, chosen to contain also heteroatoms for straightforward method validation by elemental analysis, ICP-OES, ICP-MS or NMR. In contrast to conventional labels measured bound at the particle surface, which can favor signal distortions by scattering and encoding dyes, cleavable reporters can be detected colorimetrically or fluorometrically both attached at the particle surface and after quantitative cleavage of the linker in the transparent supernatant after particle removal e.g., by centrifugation. Here, we present first results obtained for the optical quantification of carboxylic and amino groups on a series of self-made NPs with different types of labels and compare their potential and drawbacks for surface group analysis.