Analytische Chemie
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Eingeladener Vortrag
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We synthesized a generation of water-soluble, atomically precise gold nanoclusters (Au NCs) with anisotropic Surface containing a short dithiol pegylated chain (AuMHA/TDT). The AuMHA/TDT exhibit a high brightness (QY ∼ 6%) in the shortwave infrared (SWIR) spectrum with a detection above 1250 nm.
Furthermore, they show an extended half-life in blood (t1/2ß = 19.54 ± 0.05 h) and a very weak accumulation in organs. We also developed a non-invasive, whole-body vascular imaging system in the SWIR window with high-resolution, benefiting from a series of Monte Carlo image processing. The imaging process enabled to improve contrast by 1 order of magnitude and enhance the spatial Resolution by 59%. After systemic administration of these nanoprobes in mice, we can quantify vessel complexity in depth (>4 mm), allowing to detect very subtle vascular disorders non-invasively in bone morphogenetic protein 9 (Bmp9)-deficient mice. The combination of these anisotropic surface charged Au NCs plus an improved SWIR imaging device allows a precise mapping at high-resolution and an in depth understanding of the organization of the vascular network in live animals.
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.
The successful off-line coupling of asymmetrical flow field flow fractionation (AF4) and capillary electrophoresis (CE) for Separation of nanoparticles (NPs) with different surface coatings was shown.
Two mixtures of polystyrene nanoparticles (PS-NPs) with comparable core sizes (20 nm and 50 nm) but different coatings (no coating/carboxyl-coated) were studied. Separation in either method resulted in non-baseline resolved or non-separated peaks. In contrast, two-dimensional off-line coupling of AF4 and CE resulted in clearly separated regions in their 2 D plots and can obviouly improve separation resolution.
Nowadays, different nanoparticles have been developed for commercial applications. However, since data on toxicity are barely available, their increasing application in cosmetic products, food and their release in the environment might cause severe problems. Since a range of physical, chemical, and biological characteristics of NPs are closely related to particle size and surface functionalization, precise separation and surface groups quantification is essential to acquire an in-depth understanding of their properties.
In this work, the performance of asymmetrical flow field flow fractionation (AF4) and capillary electrophoresis (CE) for the separation of nanoparticles (NPs) with different sizes, coatings, and coating densities was investigated and optimized.
For the first time, a two-dimensional off-line hyphenation of both techniques (AF4-CE) was developed. The results clearly demonstrated, that AF4-CE hyphenation can significantly improve the separation resolution and reduce the peak broadening in CE. Also, for the first time, CE was employed to determine the coating density of NPs and the results were in good agreement with the values acquired with conductometric titration.
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.
Solid state multi-band emitters like lanthanide doped up-conversion nanoparticles (UCNPs) are promising materials for energy and biotechnologies. These materials are excitable in the near infrared (NIR) and show emission bands from UV to SWIR with excellent photostability, and long luminescence lifetimes in the µs range. The efficiency of these materials, i.e. the multiphoton absorption processes, the excitation power dependent population, and deactivation dynamics are strongly influenced by the particle size, structure, doping concentration, surface chemistry, and microenvironment. For applications UCNPs have to be optimized to meet the application relevant optical properties like the upconversion quantum yield (UC) and downshifting quantum yield (PL), luminescence lifetime and emission spectra.
We investigated ß-NaYF4 NPs co-doped with Yb3+ and Er3+ in aqueous and organic media and as powder. For the later, bulk and nanomaterial is compared. For dispersed particles the influence of surface chemistry (ligands), microenvironment (solvent) and size (10 to 43 nm) was studied. Especially for bioapplications the Förster-Resonance-Energy-Transfer (FRET) efficiency from UCNPs to organic dye molecules (rose bengal and sulforhodamine B) was optimized with respect to the UCNP size.
"The optical properties of semiconductor nanocrystals (SCNC) are controlled by constituent material, particle size, and surface chemistry, specifically the number of dangling bonds favoring nonradiative deactivation. This can lead to a distribution of photoluminescence Quantum yields (PL QY) amongst the SCNC particles, i.e., mixtures of “bright” and “grey” or “dark” SCNCs.
Particularly the number of absorbing, yet not emitting particles can have a significant effect on the PL quantum yield obtained in ensemble measurements, leading to ist underestimation. The “dark fraction” is not assessable in common ensemble measurements; it can be probed only on a single particle level using a confocal laser scanning microscope coupled with an AFM. Such a setup was used to study core‐shell CdSe SCNCs with different shells and surface chemistries. Special emphasis was dedicated to correlate brightness, blinking, dark fraction, and decay kinetics of the single SCNCs with the ensemble PL QY and the PL decay kinetics. The results of this study can help to identify new synthetic routes and surface modifications to colloidally and photochemically stable SCNCs with a PL QY of close to unity."
Gold nanoparticles (AuNPs) can catalyze the decolorization of organic dyes in the presence of sodium borohydride (NaBH4), which can be utilized for sensitive optical signaling. Here, we monitor the catalytic reduction of a fluorescent substrate, exemplarily chosen uranine, by AuNPs serving as nanocatalysts by absorption and fluorescence spectroscopy. Dye reduction is accompanied by dramatic changes in the absorption and fluorescence properties of uranine. As proposed reaction mechanism, we assume electron transfer between uranine and NaBH4 through the AuNPs nanocatalysts which is currently investigated also by time-resolved fluorescence and detailed spectroscopic studies of the influence of pH, NaBH4, and AuNPs on these effects. As ultimate goal, a model reporter platform with colorimetric andfluorometric signaling is anticipated for the detection of different analytes by coating AuNPs with affinity ligands such as antibodies and aptamers and and special separation methods.
Two nanosensors for simultaneous optical measurements of temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nm-sized silica-coated polystyrene nanoparticles (PS-NPs) doped with the near infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3 CrBPh4)[1][2] and an inert reference fluorescence dye (Nile Red NR or 5,10,15,20tetrakis-(pentafluorophenyl) porphyrin TFPP) and are covalently labeled with the pHsensitive fluorophore fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal distinguishable emission spectra suitable for ratiometric intensity-based and time-resolved studies in the visible and near infrared spectral region. The core-shell nanostructure of these sensors reveals high colloidal stability in various aqueous media. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of the TOP nanosensors for optically detecting the three bioanalytically and biologically relevant analytes temperature, oxygen and pH simultaneously at the same position.
Two nanosensors for simultaneous optical measurements of the bioanalytically and biologically relevant analytes temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nmsized silica-coated polystyrene nanoparticles (PS-NPs) doped with a near-infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3, CrBPh4) and an inert reference dye (Nile Red, NR or 5,10,15,20tetrakis(pentafluorophenyl) porphyrin, TFPP) and are covalently labeled with pHsensitive fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal spectrally distinguishable emission bands, allowing for ratiometric intensity-based and time-resolved studies in the visible and near-infrared wavelength region. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of these nanosensors for the sensitive luminescence readout of TOP simultaneously at the same spatialposition.