@article{MeilingCywinskiLoehmannsroeben2018,
  author    = {Meiling, Till Thomas and Cywinski, Piotr J. and L{\"o}hmannsr{\"o}ben, Hans-Gerd},
  title     = {Two-Photon excitation fluorescence spectroscopy of quantum dots},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {122},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {17},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.7b12345},
  pages     = {9641 -- 9647},
  year      = {2018},
  abstract  = {The applications of quantum dots (QDs) in two-photon (2P) excitation applications demand reliable data about their 2P absorption (2PA) cross sections (sigma(2PA)). In the present study, sigma(2PA) values have been determined for a series of commercial colloidal CdSe/ZnS QDs and CdSeTe/ZnS QDs in aqueous media. For the first time for these QDs, the sigma(2PA) values have been determined over a wide spectral range, that is, between 720 and 900 nm, and are compared to the extinction coefficient (epsilon) values obtained under one-photon (1P) excitation. Furthermore, we present a QD in combination with an organic dye in a biotin-streptavidin Forster resonance energy transfer bioassay under 1P and 2P excitation. The results for the bioassay under 2P excitation are compared to those obtained under 1P excitation. The results demonstrate that in the case of the 2P excitation, higher sensitivity can be achieved because of an improved signal-to-noise ratio.},
  language  = {en}
}
@article{WeclawskiMeilingLeniaketal.2015,
  author    = {Weclawski, Marek K. and Meiling, Till Thomas and Leniak, Arkadiusz and Cywinski, Piotr J. and Gryko, Daniel T.},
  title     = {Planar, Fluorescent Push-Pull System That Comprises Benzofuran and Iminocoumarin Moieties},
  series = {Organic letters},
  volume    = {17},
  journal   = {Organic letters},
  number    = {17},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1523-7060},
  doi       = {10.1021/acs.orglett.5b02042},
  pages     = {4252 -- 4255},
  year      = {2015},
  abstract  = {Previously unknown, vertically linked heterocycles comprised of benzofuran and iminocoumarin moieties have been synthesized directly from 1,5-dibenzoyloxyanthraquinone and arylacetonitriles via double Knoevenagel condensation followed by formal HCN elimination. The structural assembly of fully conjugated, electron-rich benzofuran and electron-deficient iminocoumarin is responsible for the strongly polarized nature of these heterocycles which translates into their polarity-sensitive fluorescence.},
  language  = {en}
}
@article{NazirMeilingCywinskietal.2015,
  author    = {Nazir, Rashid and Meiling, Till Thomas and Cywinski, Piotr J. and Gryko, Daniel T.},
  title     = {Synthesis and Optical Properties of alpha,beta-Unsaturated Ketones Bearing a Benzofuran Moiety},
  series = {Asian journal of organic chemistry : an ACES journal},
  volume    = {4},
  journal   = {Asian journal of organic chemistry : an ACES journal},
  number    = {9},
  publisher = {Wiley-VCH},
  address   = {Weinheim},
  issn      = {2193-5807},
  doi       = {10.1002/ajoc.201500242},
  pages     = {929 -- 935},
  year      = {2015},
  abstract  = {Five pi-expanded alpha,beta-unsaturated ketones have been prepared from a strongly electron-rich benzofuran derivative via Knoevenagel reaction and aldol condensation. The incorporation of two 6-didodecylaminobenzofuran-2-yl groups at the periphery of D-pi-A and D-pi-A-pi-D molecules resulted in dyes with excellent solubility in the majority of organic solvents. In contrast to the majority of alpha,beta-unsaturated ketones, these dyes emit relatively strongly in the red region with a fluorescence quantum yield up to 40\%. They also display strong solvatofluorochromism with emission shifting from 570 nm in toluene to 670 nm in CHCl3. Depending on the chemical structure, they two-photon cross-sections (sigma(2)) are up to 1700 GM (1 GM=10(50) cm(4)s photon(-1)).},
  language  = {en}
}
@misc{WessigHilleKumkeetal.2016,
  author    = {Wessig, Pablo and Hille, Carsten and Kumke, Michael Uwe and Meiling, Till Thomas and Behrends, Nicole and Eisold, Ursula},
  title     = {Two-photon FRET pairs based on coumarin and DBD dyes},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-394445},
  pages     = {33510 -- 33513},
  year      = {2016},
  abstract  = {The synthesis and photophysical properties of two new FRET pairs based on coumarin as a donor and DBD dye as an acceptor are described. The introduction of a bromo atom dramatically increases the two-photon excitation (2PE) cross section providing a 2PE-FRET system, which is also suitable for 2PE-FLIM.},
  language  = {en}
}
@phdthesis{Meiling2017,
  author    = {Meiling, Till Thomas},
  title     = {Development of a reliable and environmentally friendly synthesis for fluorescence carbon nanodots},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-410160},
  school      = {Universit{\"a}t Potsdam},
  pages     = {198},
  year      = {2017},
  abstract  = {Carbon nanodots (CNDs) have generated considerable attention due to their promising properties, e.g. high water solubility, chemical inertness, resistance to photobleaching, high biocompatibility and ease of functionalization. These properties render them ideal for a wide range of functions, e.g. electrochemical applications, waste water treatment, (photo)catalysis, bio-imaging and bio-technology, as well as chemical sensing, and optoelectronic devices like LEDs. In particular, the ability to prepare CNDs from a wide range of accessible organic materials makes them a potential alternative for conventional organic dyes and semiconductor quantum dots (QDs) in various applications. However, current synthesis methods are typically expensive and depend on complex and time-consuming processes or severe synthesis conditions and toxic chemicals. One way to reduce overall preparation costs is the use of biological waste as starting material. Hence, natural carbon sources such as pomelo peal, egg white and egg yolk, orange juice, and even eggshells, to name a few; have been used for the preparation of CNDs. While the use of waste is desirable, especially to avoid competition with essential food production, most starting-materials lack the essential purity and structural homogeneity to obtain homogeneous carbon dots. Furthermore, most synthesis approaches reported to date require extensive purification steps and have resulted in carbon dots with heterogeneous photoluminescent properties and indefinite composition. For this reason, among others, the relationship between CND structure (e.g. size, edge shape, functional groups and overall composition) and photophysical properties is yet not fully understood. This is particularly true for carbon dots displaying selective luminescence (one of their most intriguing properties), i.e. their PL emission wavelength can be tuned by varying the excitation wavelength. In this work, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain CNDs with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch, carboxylic acids and Tris-EDTA (TE) buffer as carbon- and nitrogen source, respectively. The presented microwave-assisted hydrothermal precursor carbonization (MW-hPC) is characterized by its cost-efficiency, simplicity, short reaction times, low environmental footprint, and high yields of approx. 80\% (w/w). Furthermore, only a single synthesis step is necessary to obtain homogeneous water-soluble CNDs with no need for further purification. Depending on starting materials and reaction conditions different types of CNDs have been prepared. The as-prepared CNDs exhibit reproducible, highly homogeneous and favourable PL properties with narrow emission bands (approx. 70nm FWHM), are non-blinking, and are ready to use without need for further purification, modification or surface passivation agents. Furthermore, the CNDs are comparatively small (approx. 2.0nm to 2.4nm) with narrow size distributions; are stable over a long period of time (at least one year), either in solution or as a dried solid; and maintain their PL properties when re-dispersed in solution. Depending on CND type, the PL quantum yield (PLQY) can be adjusted from as low as 1\% to as high as 90\%; one of the highest reported PLQY values (for CNDs) so far. An essential part of this work was the utilization of a microwave synthesis reactor, allowing various batch sizes and precise control over reaction temperature and -time, pressure, and heating- and cooling rate, while also being safe to operate at elevated reaction conditions (e.g. 230 ±C and 30 bar). The hereby-achieved high sample throughput allowed, for the first time, the thorough investigation of a wide range of synthesis parameters, providing valuable insight into the CND formation. The influence of carbon- and nitrogen source, precursor concentration and -combination, reaction time and -temperature, batch size, and post-synthesis purification steps were carefully investigated regarding their influence on the optical properties of as-synthesized CNDs. In addition, the change in photophysical properties resulting from the conversion of CND solution into solid and back into the solution was investigated. Remarkably, upon freeze-drying the initial brown CND-solution turns into a non-fluorescent white/slightly yellow to brown solid which recovers PL in aqueous solution. Selected CND samples were also subject to EDX, FTIR, NMR, PL lifetime (TCSPC), particle size (TEM), TGA and XRD analysis. Besides structural characterization, the pH- and excitation dependent PL characteristics (i.e. selective luminescence) were examined; giving inside into the origin of photophysical properties and excitation dependent behaviour of CNDs. The obtained results support the notion that for CNDs the nature of the surface states determines the PL properties and that excitation dependent behaviour is caused by the "Giant Red-Edge Excitation Shift" (GREES).},
  language  = {en}
}
@misc{MeilingCywińskiBald2016,
  author    = {Meiling, Till Thomas and Cywiński, Piotr J. and Bald, Ilko},
  title     = {White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-97087},
  year      = {2016},
  abstract  = {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.},
  language  = {en}
}
@article{MeilingSchuermannVogeletal.2018,
  author    = {Meiling, Till Thomas and Sch{\"u}rmann, Robin Mathis and Vogel, Stefanie and Ebel, Kenny and Nicolas, Christophe and Milosavljevic, Aleksandar R. and Bald, Ilko},
  title     = {Photophysics and Chemistry of Nitrogen-Doped Carbon Nanodots with High Photoluminescence Quantum Yield},
  series = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  volume    = {122},
  journal   = {The journal of physical chemistry : C, Nanomaterials and interfaces},
  number    = {18},
  publisher = {American Chemical Society},
  address   = {Washington},
  issn      = {1932-7447},
  doi       = {10.1021/acs.jpcc.8b00748},
  pages     = {10217 -- 10230},
  year      = {2018},
  abstract  = {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.},
  language  = {en}
}
@article{ZuehlkeMeilingRoderetal.2021,
  author    = {Z{\"u}hlke, Martin and Meiling, Till Thomas and Roder, Phillip and Riebe, Daniel and Beitz, Toralf and Bald, Ilko and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Janßen, Traute and Erhard, Marcel and Repp, Alexander},
  title     = {Photodynamic inactivation of E. coli bacteria via carbon nanodots},
  series = {ACS omega / American Chemical Society},
  volume    = {6},
  journal   = {ACS omega / American Chemical Society},
  number    = {37},
  publisher = {ACS Publications},
  address   = {Washington, DC},
  issn      = {2470-1343},
  doi       = {10.1021/acsomega.1c01700},
  pages     = {23742 -- 23749},
  year      = {2021},
  abstract  = {The increasing development of antibiotic resistance in bacteria has been a major problem for years, both in human and veterinary medicine. Prophylactic measures, such as the use of vaccines, are of great importance in reducing the use of antibiotics in livestock. These vaccines are mainly produced based on formaldehyde inactivation. However, the latter damages the recognition elements of the bacterial proteins and thus could reduce the immune response in the animal. An alternative inactivation method developed in this work is based on gentle photodynamic inactivation using carbon nanodots (CNDs) at excitation wavelengths λex > 290 nm. The photodynamic inactivation was characterized on the nonvirulent laboratory strain Escherichia coli K12 using synthesized CNDs. For a gentle inactivation, the CNDs must be absorbed into the cytoplasm of the E. coli cell. Thus, the inactivation through photoinduced formation of reactive oxygen species only takes place inside the bacterium, which means that the outer membrane is neither damaged nor altered. The loading of the CNDs into E. coli was examined using fluorescence microscopy. Complete loading of the bacterial cells could be achieved in less than 10 min. These studies revealed a reversible uptake process allowing the recovery and reuse of the CNDs after irradiation and before the administration of the vaccine. The success of photodynamic inactivation was verified by viability assays on agar. In a homemade flow photoreactor, the fastest successful irradiation of the bacteria could be carried out in 34 s. Therefore, the photodynamic inactivation based on CNDs is very effective. The membrane integrity of the bacteria after irradiation was verified by slide agglutination and atomic force microscopy. The method developed for the laboratory strain E. coli K12 could then be successfully applied to the important avian pathogens Bordetella avium and Ornithobacterium rhinotracheale to aid the development of novel vaccines.},
  language  = {en}
}
@misc{ZuehlkeMeilingRoderetal.2021,
  author    = {Z{\"u}hlke, Martin and Meiling, Till Thomas and Roder, Phillip and Riebe, Daniel and Beitz, Toralf and Bald, Ilko and L{\"o}hmannsr{\"o}ben, Hans-Gerd and Janßen, Traute and Erhard, Marcel and Repp, Alexander},
  title     = {Photodynamic Inactivation of E. coli Bacteria via Carbon Nanodots},
  series = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  journal   = {Zweitver{\"o}ffentlichungen der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe},
  publisher = {Universit{\"a}t Potsdam},
  address   = {Potsdam},
  issn      = {1866-8372},
  doi       = {10.25932/publishup-53842},
  url       = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-538425},
  pages     = {23742 -- 23749},
  year      = {2021},
  abstract  = {The increasing development of antibiotic resistance in bacteria has been a major problem for years, both in human and veterinary medicine. Prophylactic measures, such as the use of vaccines, are of great importance in reducing the use of antibiotics in livestock. These vaccines are mainly produced based on formaldehyde inactivation. However, the latter damages the recognition elements of the bacterial proteins and thus could reduce the immune response in the animal. An alternative inactivation method developed in this work is based on gentle photodynamic inactivation using carbon nanodots (CNDs) at excitation wavelengths λex > 290 nm. The photodynamic inactivation was characterized on the nonvirulent laboratory strain Escherichia coli K12 using synthesized CNDs. For a gentle inactivation, the CNDs must be absorbed into the cytoplasm of the E. coli cell. Thus, the inactivation through photoinduced formation of reactive oxygen species only takes place inside the bacterium, which means that the outer membrane is neither damaged nor altered. The loading of the CNDs into E. coli was examined using fluorescence microscopy. Complete loading of the bacterial cells could be achieved in less than 10 min. These studies revealed a reversible uptake process allowing the recovery and reuse of the CNDs after irradiation and before the administration of the vaccine. The success of photodynamic inactivation was verified by viability assays on agar. In a homemade flow photoreactor, the fastest successful irradiation of the bacteria could be carried out in 34 s. Therefore, the photodynamic inactivation based on CNDs is very effective. The membrane integrity of the bacteria after irradiation was verified by slide agglutination and atomic force microscopy. The method developed for the laboratory strain E. coli K12 could then be successfully applied to the important avian pathogens Bordetella avium and Ornithobacterium rhinotracheale to aid the development of novel vaccines.},
  language  = {en}
}
@article{MeilingCywińskiBald2016,
  author    = {Meiling, Till Thomas and Cywiński, Piotr J. and Bald, Ilko},
  title     = {White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis},
  series = {Scientific reports},
  volume    = {6},
  journal   = {Scientific reports},
  publisher = {Nature Publishing Group},
  address   = {London},
  doi       = {10.1038/srep28557},
  pages     = {9},
  year      = {2016},
  abstract  = {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.},
  language  = {en}
}