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Marko Moser, Ralf Schneider, Thomas Behnke, Thomas Schneider, Jana Falkenhagen, Ute Resch-Genger
Simple, fast, and versatile methods for the quantification of thiol groups are of considerable interest not only for protein analysis but also for the characterization of the surface chemistry of nanomaterials stabilized with thiol ligands or bearing thiol groups for the subsequent (bio-) functionalization via maleimide-thiol chemistry. Here, we compare two simple colorimetric assays, the widely used Ellman's assay performed at alkaline pH and the aldrithiol assay executed at acidic and neutral pH, with respect to their potential for the quantification of thiol groups and thiol ligands on different types of nanoparticles like polystyrene nanoparticles, semiconductor nanocrystals (SC NC), and noble metal particles, and we derive criteria for their use...
September 6, 2016: Analytical Chemistry
R Schneider, F Weigert, V Lesnyak, S Leubner, T Lorenz, T Behnke, A Dubavik, J-O Joswig, U Resch-Genger, N Gaponik, A Eychmüller
The optical properties of semiconductor nanocrystals (SC NCs) are largely controlled by their size and surface chemistry, i.e., the chemical composition and thickness of inorganic passivation shells and the chemical nature and number of surface ligands as well as the strength of their bonds to surface atoms. The latter is particularly important for CdTe NCs, which - together with alloyed CdxHg1-xTe - are the only SC NCs that can be prepared in water in high quality without the need for an additional inorganic passivation shell...
July 28, 2016: Physical Chemistry Chemical Physics: PCCP
Olga Koshkina, Dana Westmeier, Thomas Lang, Christoph Bantz, Angelina Hahlbrock, Christian Würth, Ute Resch-Genger, Ulrike Braun, Raphael Thiermann, Christoph Weise, Murat Eravci, Benjamin Mohr, Helmut Schlaad, Roland H Stauber, Dominic Docter, Annabelle Bertin, Michael Maskos
Due to the adsorption of biomolecules, the control of the biodistribution of nanoparticles is still one of the major challenges of nanomedicine. Poly(2-ethyl-2-oxazoline) (PEtOx) for surface modification of nanoparticles is applied and both protein adsorption and cellular uptake of PEtOxylated nanoparticles versus nanoparticles coated with poly(ethylene glycol) (PEG) and non-coated positively and negatively charged nanoparticles are compared. Therefore, fluorescent poly(organosiloxane) nanoparticles of 15 nm radius are synthesized, which are used as a scaffold for surface modification in a grafting onto approach...
September 2016: Macromolecular Bioscience
Pablo Darío Quevedo, Thomas Behnke, Ute Resch-Genger
Aiming at the development of validated protocols for protein conjugation of nanomaterials and the determination of protein labeling densities, we systematically assessed the conjugation of the model protein streptavidin (SAv) to 100-, 500-, and 1000-nm-sized polystyrene and silica nanoparticles and dye-encoded polymer particles with two established conjugation chemistries, based upon achievable coupling efficiencies and labeling densities. Bioconjugation reactions compared included EDC/sulfo NHS ester chemistry for direct binding of the SAv to carboxyl groups at the particle surface and maleimide-thiol chemistry in conjunction with heterobifunctional PEG linkers and aminated nanoparticles (NPs)...
June 2016: Analytical and Bioanalytical Chemistry
Markus Grabolle, Marian Starke, Ute Resch-Genger
Nanoclays like laponites, which are commercially avaible in large quantities for a very moderate price, provide a facile solubilization strategy for hydrophobic dyes without the need for chemical functionalization and can act as a carrier for a high number of dye molecules. This does not require reactive dyes, amplifies fluorescence signals from individual emitters due to the high number of dyes molecules per laponite disk, and renders hydrophobic emitters applicable in aqueous environments. Aiming at the rational design of bright dye-loaded nanoclays as a new class of fluorescent reporters for bioanalysis and material sciences and the identification of dye structure-property relationships, we screened a series of commercial fluorescent dyes, differing in dye class, charge, and character of the optical transitions involved, and studied the changes of their optical properties caused by clay adsorption at different dye loading concentrations...
April 12, 2016: Langmuir: the ACS Journal of Surfaces and Colloids
Jagoda Sloniec-Myszk, Ute Resch-Genger, Andreas Hennig
Enzyme-activatable optical probes are important for future advances in cancer imaging, but may easily suffer from low signal-to-background ratios unless not optimized. To address this shortcoming, numerous mechanisms to modulate the fluorescence signal have been explored. We report herein newly synthesized probes based on self-immolative linkers containing chiral J-aggregate-forming dyes. Signal modulation by formation of chiral J-aggregates is yet unexplored in optical enzyme probe design. The comprehensive characterization of the probes by absorption, CD, fluorescence, and time-resolved fluorescence spectroscopy revealed dye-dye interactions not observed for the free dyes in solution as well as dye-protein interactions with the enzyme...
February 11, 2016: Journal of Physical Chemistry. B
Gert Roebben, Vikram Kestens, Zoltan Varga, Jean Charoud-Got, Yannic Ramaye, Christian Gollwitzer, Dorota Bartczak, Daniel Geißler, James Noble, Stephane Mazoua, Nele Meeus, Philippe Corbisier, Marcell Palmai, Judith Mihály, Michael Krumrey, Julie Davies, Ute Resch-Genger, Neelam Kumarswami, Caterina Minelli, Aneta Sikora, Heidi Goenaga-Infante
This paper describes the production and characteristics of the nanoparticle test materials prepared for common use in the collaborative research project NanoChOp (Chemical and optical characterization of nanomaterials in biological systems), in casu suspensions of silica nanoparticles and CdSe/CdS/ZnS quantum dots (QDs). This paper is the first to illustrate how to assess whether nanoparticle test materials meet the requirements of a "reference material" (ISO Guide 30, 2015) or rather those of the recently defined category of "representative test material (RTM)" (ISO/TS 16195, 2013)...
2015: Frontiers in Chemistry
M Andrea Markus, Joanna Napp, Thomas Behnke, Miso Mitkovski, Sebastian Monecke, Christian Dullin, Stephen Kilfeather, Ralf Dressel, Ute Resch-Genger, Frauke Alves
Molecular imaging of inflammatory lung diseases, such as asthma, has been limited to date. The recruitment of innate immune cells to the airways is central to the inflammation process. This study exploits these cells for imaging purposes within the lung, using inhaled polystyrene nanoparticles loaded with the near-infrared fluorescence dye Itrybe (Itrybe-NPs). By means of in vivo and ex vivo fluorescence reflectance imaging of an ovalbumin-based allergic airway inflammation (AAI) model in hairless SKH-1 mice, we show that subsequent to intranasal application of Itrybe-NPs, AAI lungs display fluorescence intensities significantly higher than those in lungs of control mice for at least 24 h...
December 22, 2015: ACS Nano
Xu Wang, Jutta Pauli, Reinhard Niessner, Ute Resch-Genger, Dietmar Knopp
A multifunctional fluorescence platform has been constructed based on gold nanoparticle (AuNP)-catalyzed uranine reduction. The catalytic reduction of uranine was conducted in aqueous solution using AuNPs as nanocatalyst and sodium borohydride as reducing reagent, which was monitored by fluorescence and UV-vis spectroscopy. The reaction rate was highly dependent on the concentration, size and dispersion state of AuNPs. When AuNPs aggregated, their catalytic ability decreased, and thereby a label-free fluorescent assay was developed for the detection of melamine, which can be used for melamine determination in milk...
November 7, 2015: Analyst
Marko Moser, Thomas Behnke, Carolina Hamers-Allin, Karin Klein-Hartwig, Jana Falkenhagen, Ute Resch-Genger
The surface modification of nanometer- and micrometer-sized particles and planar substrates with polyethylene glycol (PEG) ligands of varying length is a very common strategy to tune the hydrophilicity and biocompatibility of such materials, minimize unspecific interactions, improve biofunctionalization efficiencies, and enhance blood circulation times. Nevertheless, simple methods for the quantification of PEG ligands are comparatively rare. Here, we present a new concept for the quantification of PEG ligands for maleimide-functionalized PEG molecules and the determination of PEG coupling efficiencies, exploiting the quantitative reaction of maleimide with l-cysteine, and the subsequent determination of the unreacted thiol with the photometric Ellman's test...
September 15, 2015: Analytical Chemistry
Sven Otto, Markus Grabolle, Christoph Förster, Christoph Kreitner, Ute Resch-Genger, Katja Heinze
Bright, long-lived emission from first-row transition-metal complexes is very challenging to achieve. Herein, we present a new strategy relying on the rational tuning of energy levels. With the aid of the large N-Cr-N bite angle of the tridentate ligand ddpd (N,N'-dimethyl-N,N'-dipyridine-2-ylpyridine-2,6-diamine) and its strong σ-donating capabilities, a very large ligand-field splitting could be introduced in the chromium(III) complex [Cr(ddpd)2](3+), that shifts the deactivating and photoreactive (4)T2 state well above the emitting (2)E state...
September 21, 2015: Angewandte Chemie
Riikka Arppe, Iko Hyppänen, Niina Perälä, Riikka Peltomaa, Martin Kaiser, Christian Würth, Simon Christ, Ute Resch-Genger, Michael Schäferling, Tero Soukka
We have studied the mechanisms of water-based quenching of the upconversion photoluminescence of upconverting nanophosphors (UCNPs) via luminescence decay measurements for a better understanding of the non-radiative deactivation pathways responsible for the relatively low upconversion luminescence efficiency in aqueous solutions. This included both upconversion luminescence measurements and the direct excitation of emissive energy states of Er(3+) and Yb(3+) dopants in NaYF4:Yb(3+),Er(3+) UCNPs by measuring the decays at 550 and 655 nm upon 380 nm excitation and at 980 nm upon 930 nm excitation, respectively...
July 21, 2015: Nanoscale
Katrin Hoffmann, Monika Spieles, Wolfram Bremser, Ute Resch-Genger
The development of a lanthanum-phosphate glass doped with several rare-earth-ions for use as solid fluorescence standard is described. The cuvette-shaped reference material which shows a characteristic emission intensity pattern upon excitation at 365 nm consisting of a multitude of relatively narrow emission bands in the wavelength region between 450 and 700 nm is intended for the day-to-day performance validation of fluorescence measuring devices. Evaluation of the fluorescent glass includes the determination of all properties which can affect its relative emission intensity profile or contribute to the uncertainty of the certified values like absorption spectra, fluorescence anisotropy, excitation wavelength, and temperature dependence of the spectroscopic features, homogeneity of fluorophore distribution, and photo- and long-term stability...
July 21, 2015: Analytical Chemistry
Christian Würth, Ute Resch-Genger
The ever-increasing use of fluorescent nanomaterials and micrometer-sized beads in the life and material sciences requires reliable procedures for the measurement of the key performance parameter fluorescence quantum yield (Φf) of scattering particle dispersions and reference systems to evaluate the performance of such measurements. This encouraged us to systematically study, both theoretically and experimentally, the optical determination of photoluminescent quantum yield as a function of the scattering and absorption properties of the sample and the illumination geometry with an integrating sphere method...
June 2015: Applied Spectroscopy
Tom Felbeck, Simon Mundinger, Marina M Lezhnina, Mark Staniford, Ute Resch-Genger, Ulrich H Kynast
Valuable emissive properties of organic fluorophores have become indispensable analytical tools in biophotonics, but frequently suffer from low solubilities and radiationless deactivation in aqueous media, that is, in biological ambience as well. In this report, nanoscaled dye-clay hybrids based on laponite, Na0.7 {(Li0.3 Mg5.5 )[Si8 O20 (OH)4 ]}, are taken advantage of to solubilize neutral dyes, which are natively not encountered in water. Previously reported efficiency and solubility bottlenecks of such hybrids can to a large extent be overcome by comparably simple chemical measures, as demonstrated here for two prominent examples, the fluorescent dyes Nile Red and Coumarin 153...
May 11, 2015: Chemistry: a European Journal
Virginia Wycisk, Jutta Pauli, Pia Welker, Aileen Justies, Ute Resch-Genger, Rainer Haag, Kai Licha
The synthesis of water-soluble dyes, which absorb and emit in the range between 650 and 950 nm and display high extinction coefficients (ε) as well as high fluorescence quantum yields (Φf), is still a demand for optical imaging. We now present a synthetic route for the preparation of a new group of glycerol-substituted cyanine dyes from dendronized indole precursors that have been functionalized as N-hydroxysuccinimide (NHS) esters. High Φf values of up to 0.15 and extinction coefficients of up to 189 000 L mol(-1) cm(-1) were obtained for the pure dyes...
April 15, 2015: Bioconjugate Chemistry
Andreas Hennig, Paul M Dietrich, Felix Hemmann, Thomas Thiele, Heike Borcherding, Angelika Hoffmann, Uwe Schedler, Christian Jäger, Ute Resch-Genger, Wolfgang E S Unger
The fluorine content of polymer particles labelled with 2,2,2-trifluoroethylamine was reliably quantified with overlapping sensitivity ranges by XPS and solid-state NMR. This provides a first step towards reference materials for the metrological traceability of surface group quantifications. The extension of this concept to fluorescence spectroscopy is illustrated.
March 21, 2015: Analyst
C Brunner, K Hoffmann, T Thiele, U Schedler, H Jehle, U Resch-Genger
Commercial platforms consisting of ready-to-use microarrays printed with target-specific DNA probes, a microarray scanner, and software for data analysis are available for different applications in medical diagnostics and food analysis, detecting, e.g., viral and bacteriological DNA sequences. The transfer of these tools from basic research to routine analysis, their broad acceptance in regulated areas, and their use in medical practice requires suitable calibration tools for regular control of instrument performance in addition to internal assay controls...
April 2015: Analytical and Bioanalytical Chemistry
Stefan Wilhelm, Martin Kaiser, Christian Würth, Josef Heiland, Carolina Carrillo-Carrion, Verena Muhr, Otto S Wolfbeis, Wolfgang J Parak, Ute Resch-Genger, Thomas Hirsch
We present a systematic study on the effect of surface ligands on the luminescence properties and colloidal stability of β-NaYF4:Yb(3+),Er(3+) upconversion nanoparticles (UCNPs), comparing nine different surface coatings to render these UCNPs water-dispersible and bioconjugatable. A prerequisite for this study was a large-scale synthetic method that yields ∼2 g per batch of monodisperse oleate-capped UCNPs providing identical core particles. These ∼23 nm sized UCNPs display an upconversion quantum yield of ∼0...
January 28, 2015: Nanoscale
C Würth, D Geissler, T Behnke, M Kaiser, U Resch-Genger
A crucial variable for methodical performance evaluation and comparison of luminescent reporters is the photoluminescence quantum yield (Φ pl). This quantity, defined as the number of emitted photons per number of absorbed photons, is the direct measure of the efficiency of the conversion of absorbed photons into emitted light for small organic dyes, fluorescent proteins, metal-ligand complexes, metal clusters, polymeric nanoparticles, and semiconductor and up-conversion nanocrystals. Φ pl determines the sensitivity for the detection of a specific analyte from the chromophore perspective, together with its molar-absorption coefficient at the excitation wavelength...
January 2015: Analytical and Bioanalytical Chemistry
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