TY - JOUR A1 - Wegner, Karl David A1 - Dussert, F. A1 - Truffier-Boutry, D. A1 - Benayad, A. A1 - Beal, D. A1 - Mattera, L. A1 - Ling, W. L. A1 - Carrière, M. A1 - Reiss, P. T1 - Influence of the Core/Shell Structure of Indium Phosphide Based Quantum Dots on Their Photostability and Cytotoxicity JF - Frontiers in Chemistry N2 - With the goal to improve their photostability, InP-based QDs are passivated with three types of inorganic shells, namely (i) a gradient ZnSexS1−x shell, (ii) an additional ZnS shell on top of the gradient shell with two different thicknesses (core/shell/shell, CSS), (iii) an alumina coating on top of ZnS. All three systems have photoluminescence Quantum yields (PLQY) > 50%and similar PL decay times (64–67 ns). To assess their photostability they are incorporated into a transparent poly (methyl methacrylate) (PMMA) matrix and exposed to continuous irradiation with simulated sunlight in a climate chamber. The alumina coated core/shell system exhibits the highest stability in terms of PLQY Retention as well as the lowest shift of the PL maximum and lowest increase of the PL linewidth, followed by the CSS QDs and finally the gradient shell system. By means of XPS studies we identify the degradation of the ZnS outer layer and concomitant xidation of the emissive InZnP core as the main origins of degradation in the gradient structure. These modifications do not occur in the case of the alumina-capped sample, which exhibits excellent chemical stability. The gradient shell and CSS systems could be transferred to the aqueous phase using surface ligand exchange with penicillamine. Cytotoxicity studies on human primary keratinocytes revealed that exposure for 24 h to 6.25–100 nM of QDs did not affect cell viability. However, a trend toward reduced cell proliferation is observed for higher concentrations of gradient shell and CSS QDs with a thin ZnS shell, while CSS QDs with a thicker ZnS shell do not exhibit any impact. KW - Indium phosphide KW - Quantum dots KW - Cytotoxicity KW - Photostability PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-494249 DO - https://doi.org/10.3389/fchem.2019.00466 VL - 7 SP - Article Number: 466 PB - Frontiers Media SA AN - OPUS4-49424 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Dhamo, Lorena A1 - Wuerth, Christian A1 - Soares, J. A1 - Resch-Genger, Ute T1 - Synthesis and optical characterization of ternary Quantum Dots: AgInS /ZnS N2 - Ternary semiconductors quantum dots (t-QD) are Cd-free nanocrystals made from I-III-VI group elements like silver or copper, indium and sulfide yielding CIS (CuInS2) or AIS (AgInS2) QDs. They are interesting alternatives to Cd-based QDs for applications as solar concentrators or optically active material for solar cells, light emitting diodes (LED) or reporters for diagnostic assays. To avoid ligand exchange procedures for high quality QDs, commonly synthesized in high boiling apolar solvents with apolar surface ligands, AIS QDs are synthesized in aqueous solution, required for bioanalytical application, by a microwave-assisted procedure. The surface of these QDs is passivated by a ZnS shell to enhance photoluminescence quantum yield (PL QY) and prevent material decomposition and oxidation. The resulting AIS/ZnS QDs exhibit broad PL spectra in the visible and near infrared, tunable by size and chemical composition. I will show the simple synthetic procedure and a spectroscopic study of different AIS QDs evaluating their PL properties and stability, PL QY, and PL decay kinetics. The analyzed sample showed long lifetimes, relatively high QY (50%) and good stability. Ligand conjugation is also performed to allow the embedding in polymer matrix, which requires apolar cappng. The simple aqueous synthesis together with the tunable emission color, the high PL QY, the high absorption coefficients and the long luminescence lifetimes make these t-QDs promising Cd-free materials for many different applications in the material and life sciences. T2 - NanoWorkshop CY - Berlin, Germany DA - 14.05.2018 KW - Synthesis KW - Quantum dots KW - Optical spectroscopy PY - 2018 AN - OPUS4-45115 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Resch-Genger, Ute T1 - Optical spectroscopy – Techniques, instrumentation, and typical molecular and nanoscale reporters N2 - Different types of optical spectroscopies are introduced with special emphasis on method-inherent limitations and reliable instrument calibration and performance validation. In addition, different classes of molecular and nanocrystalline emitters are presented and the underlying photophysical processes are briefly described. T2 - Fakultät der University of Ottawa CY - Ottawa, Canada DA - 11.12.2018 KW - quality assurcance KW - Optical spectroscopy KW - Method comparison KW - Photoluminescence KW - Calibration KW - Performance validation KW - Dye KW - Nanoparticle KW - Quantum dots KW - Quantum yields KW - Uncertainty KW - Method validation PY - 2018 AN - OPUS4-47631 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CHAP A1 - Gawlitza, Kornelia A1 - Wan, Wei A1 - Wagner, Sabine A1 - Rurack, Knut ED - Tiwari, Ashutosh ED - Uzun, Lokman T1 - Fluorescent Molecularly Imprinted Polymers T2 - Advanced Molecularly Imprinting Materials N2 - An ideal sensor system is a combination of a selective receptor, an effective transducer, and a sensitive detector. To utilize molecularly imprinted polymers (MIPs) as responsive recognition phases in sensors, the employment of fluorescent molecules or nanoparticles (NPs) that show prominent changes in their spectroscopic properties after binding of the target molecule in the MIP’s cavity is particularly attractive. Such fluorescent MIPs (fMIPs) act through target-induced quenching, enhancement, or spectral shifts of the fluorescence. This contribution introduces different strategies of incorporation of fluorescent dyes, probes, and NPs into fMIPs. In addition, various sensing mechanisms are reviewed, and depending on the application of the sensor, the different deployable formats, their advantages, drawbacks, and impact will be presented and discussed. KW - Dyes KW - Fluorescence KW - Molecular imprinted polymers KW - Quantum dots KW - Sensors PY - 2017 SN - 978-1-119-33629-7 SP - 89 EP - 128 PB - Scrivener Publishing, WILEY CY - Beverly, MA ET - 1 AN - OPUS4-38798 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schneider, Ralf A1 - Weigert, Florian A1 - Lesnyak, V. A1 - Leubner, S. A1 - Lorenz, T. A1 - Behnke, Thomas A1 - Dubavik, A. A1 - Joswig, J.-O. A1 - Resch-Genger, Ute A1 - Gaponik, N. A1 - Eychmüller, A. ED - Resch-Genger, Ute ED - Schneider, Ralf T1 - pH and concentration dependence of the optical properties of thiol-capped CdTe nanocrystals in water and D2O JF - Physical Chemistry Chemical Physics N2 - 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. Aiming at a better understanding of the role of stabilizing ligands for the control of the application-relevant fluorescence features of SC NCs, we assessed the influence of two of the most commonly used monodentate thiol ligands, thioglycolic acid (TGA) and mercaptopropionic acid (MPA), on the colloidal stability, photoluminescence (PL) quantum yield (QY), and PL decay behavior of a set of CdTe NC colloids. As an indirect measure for the strength of the coordinative bond of the ligands to SC NC surface atoms, the influence of the pH (pD) and the concentration on the PL properties of these colloids was examined in water and D₂O and compared to the results from previous dilution studies with a set of thiol-capped Cd₁₋ₓHgₓTe SC NCs in D₂O. As a prerequisite for these studies, the number of surface ligands was determined photometrically at different steps of purification after SC NC synthesis with Ellman’s test. Our results demonstrate ligand control of the pH-dependent PL of these SC NCs, with MPA-stabilized CdTe NCs being less prone to luminescence quenching than TGA-capped ones. For both types of CdTe colloids, ligand desorption is more pronounced in H₂O compared to D₂O, underlining also the role of hydrogen bonding and solvent molecules. KW - Quantum dots KW - Fluorescence KW - Ligand analysis KW - Nano particles PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-371253 DO - https://doi.org/10.1039/c6cp03123d VL - 18 IS - 28 SP - 19083 EP - 19092 PB - RSC CY - Cambridge AN - OPUS4-37125 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Potapkin, D. V. A1 - Geißler, Daniel A1 - Resch-Genger, Ute A1 - Goryacheva, I. Y. T1 - Fluorescent quantum dot hydrophilization with PAMAM dendrimer JF - Journal of Nanoparticle Research N2 - Polyamidoamine (PAMAM) dendrimers were used to produce CdSe core/multi-shell fluorescent quantum dots (QDs) which are colloidally stable in aqueous solutions. The size, charge, and optical properties of QDs functionalized with the 4th (G4) and 5th (G5) generation of PAMAM were compared with amphiphilic polymer-covered QDs and used as criteria for the evaluation of the suitability of both water solubilization methods. As revealed by dynamic and electrophoretic light scattering (DLS and ELS), the hydrodynamic sizes of the QDs varied from 30 to 65 nm depending on QD type and dendrimer generation, with all QDs displaying highly positive surface charges, i.e., zeta potentials of around +50 mV in water. PAMAM functionalization yielded stable core/multi-shell QDs with photoluminescence quantum yields (Φ) of up to 45%. These dendrimer-covered QDs showed a smaller decrease in their Φ upon phase transfer compared with QDs made water soluble via encapsulation with amphiphilic brush polymer bearing polyoxyethylene/ polyoxypropylene chains. KW - Photoluminescence quantum yield KW - Quantum dots KW - PAMAM dendrimers KW - Phase transfer KW - Fluorescence PY - 2016 DO - https://doi.org/10.1007/s11051-016-3411-4 VL - 18 IS - 108 SP - 1 EP - 9 PB - Springer Science + Business Media B.V. CY - Dordrecht, Netherlands AN - OPUS4-35857 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Leiterer, Jork A1 - Grabolle, Markus A1 - Rurack, Knut A1 - Resch-Genger, Ute A1 - Ziegler, J. A1 - Nann, T. A1 - Panne, Ulrich T1 - Acoustically Levitated Droplets - A Contactless Sampling Method for Fluorescence Studies JF - Annals of the New York academy of sciences N2 - Acoustic levitation is used as a newtool to study concentration-dependent processes influorescence spectroscopy. With this technique, small amounts of liquid and solid samples can be measured without the need for sample supports or containers, which often limits signal acquisition and can even alter sample properties due to interactions with the support material. We demonstrate that, because of the small sample volume, fluorescence measurements at high concentrations of an organic dye are possible without the limitation of inner-filter effects, which hamper such experiments in conventional, cuvette-based measurements. Furthermore, we show that acoustic levitation of liquid samples provides an experimentally simple way to study distance-dependent fluorescence modulations in semiconductor nanocrystals. The evaporation of the solvent during levitation leads to a continuous increase of solute concentration and can easily be monitored by laser-induced fluorescence. KW - Acoustic levitation KW - Dyes KW - Energy transfer KW - Fluorescence KW - Quantum dots KW - Nanocrystals KW - Ultrasonic trap PY - 2008 DO - https://doi.org/10.1196/annals.1430.039 SN - 0077-8923 SN - 1749-6632 SN - 0094-8500 VL - 1130 SP - 78 EP - 84 PB - New York Academy of Sciences CY - New York, NY AN - OPUS4-17658 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -