TY - JOUR A1 - Meiling, T. T. A1 - Schürmann, Robin A1 - Vogel, Stefanie A1 - Ebel, Kenny A1 - Nicolas, C. A1 - Milosavljević, A. R. A1 - Bald, Ilko T1 - Photophysics and chemistry of nitrogen-doped carbon nanodots with high photoluminescence quantum yield N2 - Fluorescent carbon nanodots (CNDs) are very promising nanomaterials for a broad range of applications because of their high photostability, presumed selective luminescence, and low cost at which they can be produced. In this respect, CNDs are superior to well-established semiconductor quantum dots and organic dyes. However, reported synthesis protocols for CNDs typically lead to low photoluminescence quantum yield (PLQY) and low reproducibility, resulting in a poor understanding of the CND chemistry and photophysics. Here, we report a one-step synthesis of nitrogen-doped carbon nanodots (N-CNDs) from various carboxylic acids, Tris, and ethylenediaminetetraacetic acid resulting in high PLQY of up to 90%. The reaction conditions in terms of starting materials, temperature, and reaction time are carefully optimized and their influence on the photophysical properties is characterized. We find that citric acid-derived N-CNDs can result in a very high PLQY of 90%, but they do not Show selective luminescence. By contrast, acetic acid-derived N-CNDs show selective luminescence but a PLQY of 50%. The chemical composition of the surface and core of these two selected N-CND types is characterized among others by high-Resolution synchrotron X-ray photoelectron spectroscopy using single isolated N-CND clusters. The results indicate that photoexcitation occurs in the N-CND core, whereas the emission properties are determined by the N-CND surface groups. KW - Carbon nanodots KW - Fluorescence KW - Synchrotron XPS PY - 2018 DO - https://doi.org/10.1021/acs.jpcc.8b00748 SN - 1932-7447 VL - 122 IS - 18 SP - 10217 EP - 10230 PB - American Chemical Society CY - Washington, DC AN - OPUS4-45426 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meiling, T. A1 - Cywinski, P. A1 - Bald, Ilko T1 - White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis N2 - In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly Brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst. KW - Carbon dots KW - Quantum yield KW - Fluorescence KW - Nanoparticles PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-367204 DO - https://doi.org/10.1038/srep28557 VL - 6 SP - Article 28557, 1 EP - 9 PB - Nature Publishing Group AN - OPUS4-36720 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Vogel, Stefanie A1 - Ebel, Kenny A1 - Schürmann, Robin M. A1 - Heck, Christian A1 - Meiling, T. A1 - Milosavljevic, A. A1 - Giuliani, A. A1 - Bald, Ilko T1 - Vacuum-UV and low-energy electron induced DNA strand breaks - Influence of the DNA sequence and substrate N2 - DNA is effectively damaged by radiation, which can on the one hand lead to cancer and is on the other hand directly exploited in the treatment of tumor tissue. DNA strand breaks are already induced by photons having an energy below the ionization energy of DNA. At high photon energies, most of the DNA strand breaks are induced by low-energy secondary electrons. In the present study we quantified photon and electron induced DNA strand breaks in four different 12mer oligonucleotides. They are irradiated directly with 8.44 eV vacuum ultraviolet (VUV) photons and 8.8 eV low energy electrons (LEE). By using Si instead of VUV transparent CaF2 as a substrate the VUV exposure leads to an additional release of LEEs, which have a maximum energy of 3.6 eV and can significantly enhance strand break cross sections. Atomic force microscopy is used to visualize strand breaks on DNA origami platforms and to determine absolute values for the strand break cross sections. Upon irradiation with 8.44 eV photons all the investigated sequences show very similar strand break cross sections in the range of 1.7 - 2.3 x 10-16 cm2. The strand break cross sections for LEE irradiation at 8.8 eV are one to two orders of magnitude larger than the ones for VUV photons, and a slight sequence dependence is observed. The sequence dependence is even more pronounced for LEEs with energies < 3.6 eV. The present results help to assess DNA damage by photons and electrons close to the ionization threshold. KW - Vacuum-UV KW - Low-Energy KW - DNA KW - DNA-Sequence PY - 2019 DO - https://doi.org/10.1002/cphc.201801152 SN - 1439-7641 VL - 20 IS - 6 SP - 823 EP - 830 PB - WILEY-VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-47464 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -