@article{EisoldKupstatKlieretal.2014, author = {Eisold, Ursula and Kupstat, Annette and Klier, Dennis Tobias and Primus, Philipp-A. and Pschenitza, Michael and Niessner, Reinhard and Knopp, Dietmar and Kumke, Michael Uwe}, title = {Probing the physicochemical interactions of 3-hydroxy-benzo[a]pyrene with different monoclonal and recombinant antibodies by use of fluorescence line-narrowing spectroscopy}, series = {Analytical \& bioanalytical chemistry}, volume = {406}, journal = {Analytical \& bioanalytical chemistry}, number = {14}, publisher = {Springer}, address = {Heidelberg}, issn = {1618-2642}, doi = {10.1007/s00216-013-7584-8}, pages = {3387 -- 3394}, year = {2014}, abstract = {Characterization of interactions between antigens and antibodies is of utmost importance both for fundamental understanding of the binding and for development of advanced clinical diagnostics. Here, fluorescence line-narrowing (FLN) spectroscopy was used to study physicochemical interactions between 3-hydroxybenzo[a]pyrene (3OH-BaP, as antigen) and a variety of solvent matrices (as model systems) or anti-polycyclic aromatic hydrocarbon antibodies (anti-PAH). We focused the studies on the specific physicochemical interactions between 3OH-BaP and different, previously obtained, monoclonal and recombinant anti-PAH antibodies. Control experiments performed with non-binding monoclonal antibodies and bovine serum albumin (BSA) indicated that nonspecific interactions did not affect the FLN spectrum of 3OH-BaP. The spectral positions and relative intensities of the bands in the FLN spectra are highly dependent on the molecular environment of the 3OH-BaP. The FLN bands correlate with different vibrational modes of 3OH-BaP which are affected by interactions with the molecular environment (pi-pi interactions, H-bonding, or van-der-Waals forces). Although the analyte (3OH-BaP) was the same for all the antibodies investigated, different binding interactions could be identified from the FLN spectra on the basis of structural flexibility and conformational multiplicity of the antibodies' paratopes.}, language = {en} } @article{EisoldSellrieMemczaketal.2018, author = {Eisold, Ursula and Sellrie, Frank and Memczak, Henry and Andersson, Anika and Schenk, J{\"o}rg A. and Kumke, Michael Uwe}, title = {Dye tool box for a fluorescence enhancement immunoassay}, series = {Bioconjugate chemistry}, volume = {29}, journal = {Bioconjugate chemistry}, number = {1}, publisher = {American Chemical Society}, address = {Washington}, issn = {1043-1802}, doi = {10.1021/acs.bioconjchem.7b00731}, pages = {203 -- 214}, year = {2018}, abstract = {Immunochemical analytical methods are very successful in clinical diagnostics and are nowadays also emerging in the control of food as well as monitoring of environmental issues. Among the different immunoassays, luminescence based formats are characterized by their outstanding sensitivity making this format especially attractive for future applications. The need for multiparameter detection capabilities calls for a tool box of dye labels in order to transduce the biochemical reaction into an optically detectable signal. Here, in a multiparameter approach each analyte may be detected by a different dye with a unique emission color (covering the blue to red spectral range) or a unique luminescence decay kinetics. In the case of a competitive immunoassay format for each of the different dye labels an individual antibody would be needed. In the present paper a slightly modified approach is presented using a 7-aminocoumarin unit as the basic antigen against which highly specific antibodies were generated. Leaving the epitope region in the dyes unchanged but introducing a side group in positon 3 of the coumarin system allowed us to tune the optical properties of the coumarin dyes without the necessity of new antibody generation. Upon modification of the parent coumarin unit the full spectral range from blue to deep red was accessed. In the manuscript the photophysical characterization of the coumarin derivatives and their corresponding immunocomplexes with two highly specific antibodies is presented. The coumarin dyes and their immunocomplexes were characterized by steady-state and time-resolved absorption as well as emission spectroscopy. Moreover, fluorescence depolarization measurements were carried out to complement the data stressing the different binding modes of the two antibodies. The binding modes were evaluated using the photophysics of 7-aminocoumarins and how it was affected in the respective immunocomplexes, namely, the formation of the intramolecular charge transfer (ICT) as well as the twisted intramolecular charge transfer (TICT). In contrast to other antibody-dye pairs reported a distinct fluorescence enhancement upon formation of the antibody-dye complex up to a factor of SO was found. Because of the easy emission color tuning by tailoring the coumarin substitution for the antigen binding in nonrelevant position 3 of the parent molecule, a dye tool box is on hand which can be used in the construction of competitive multiparameter fluorescence enhancement immunoassays (FenIA).}, language = {en} } @article{EisoldSellrieSchenketal.2015, author = {Eisold, Ursula and Sellrie, Frank and Schenk, J{\"o}rg A. and Lenz, Christine and St{\"o}cklein, Walter F. M. and Kumke, Michael Uwe}, title = {Bright or dark immune complexes of anti-TAMRA antibodies for adapted fluorescence-based bioanalysis}, series = {Analytical \& bioanalytical chemistry}, volume = {407}, journal = {Analytical \& bioanalytical chemistry}, number = {12}, publisher = {Springer}, address = {Heidelberg}, issn = {1618-2642}, doi = {10.1007/s00216-015-8538-0}, pages = {3313 -- 3323}, year = {2015}, abstract = {Fluorescence labels, for example fluorescein or rhodamin derivatives, are widely used in bioanalysis applications including lateral-flow assays, PCR, and fluorescence microscopy. Depending on the layout of the particular application, fluorescence quenching or enhancement may be desired as the detection principle. Especially for multiplexed applications or high-brightness requirements, a tunable fluorescence probe can be beneficial. The alterations in the photophysics of rhodamine derivatives upon binding to two different anti-TAMRA antibodies were investigated by absorption and fluorescence-spectroscopy techniques, especially determining the fluorescence decay time and steady-state and time-resolved fluorescence anisotropy. Two monoclonal anti-TAMRA antibodies were generated by the hybridoma technique. Although surface-plasmon-resonance measurements clearly proved the high affinity of both antibodies towards 5-TAMRA, the observed effects on the fluorescence of rhodamine derivatives were very different. Depending on the anti-TAMRA antibody either a strong fluorescence quenching (G71-DC7) or a distinct fluorescence enhancement (G71-BE11) upon formation of the immune complex was observed. Additional rhodamine derivatives were used to gain further information on the binding interaction. The data reveal that such haptens as 5-TAMRA could generate different paratopes with equal binding affinities but different binding interactions, which provide the opportunity to adapt bioanalysis methods including immunoassays for optimized detection principles for the same hapten depending on the specific requirements.}, language = {en} } @misc{EngelhardKumkeLoehmannsroeben2006, author = {Engelhard, Sonja and Kumke, Michael Uwe and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {OPQS - optical process and quality sensing : exemplary applications in the beerbrewing and polyurethane foaming processes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12191}, year = {2006}, abstract = {Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near-infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant.}, language = {en} } @article{EngelhardKumkeLoehmannsroeben2006, author = {Engelhard, Sonja and Kumke, Michael Uwe and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Examples of the application of optical process and quality sensing (OPQS) to beer brewing and polyurethane foaming processes}, issn = {1618-2642}, doi = {10.1007/s00216-005-3364-4}, year = {2006}, abstract = {Optical methods play an important role in process analytical technologies (PAT). Four examples of optical process and quality sensing (OPQS) are presented, which are based on three important experimental techniques: near- infrared absorption, luminescence quenching, and a novel method, photon density wave (PDW) spectroscopy. These are used to evaluate four process and quality parameters related to beer brewing and polyurethane (PU) foaming processes: the ethanol content and the oxygen (O-2) content in beer, the biomass in a bioreactor, and the cellular structures of PU foam produced in a pilot production plant}, language = {en} } @misc{FrimmelKumke1998, author = {Frimmel, Fritz Hartmann and Kumke, Michael Uwe}, title = {Optische Parameter zur Stoffcharakterisierung vom Trinkwasser bis zum Abwasser}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-13088}, year = {1998}, abstract = {Die Anwendung von optischen Parametern zur Stoffcharakterisierung wird diskutiert. Dabei ist der Schwerpunkt der Diskussion auf absorptions- und fluoreszenzspektroskopische Methoden gesetzt. Beide Methoden k{\"o}nnen schnell und zuverl{\"a}ssig - auch im on-line Betrieb - eingesetzt werden. Der Beitrag soll einen {\"U}berblick {\"u}ber die grundlegenden M{\"o}glichkeiten der Anwendung beider Methoden geben.}, language = {de} } @article{GehneFlehrKienzleretal.2012, author = {Gehne, S{\"o}ren and Flehr, Roman and Kienzler, Andrea Altevogt Nee and Berg, Maik and Bannwarth, Willi and Kumke, Michael Uwe}, title = {Dye dynamics in three-color FRET samples}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {116}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {35}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp3064273}, pages = {10798 -- 10806}, year = {2012}, abstract = {Time-resolved emission data (fluorescence decay and fluorescence depolarization) of two three-color Forster resonance energy transfer (tc-FRET) systems consisting of a carbostyril donor (D), a ruthenium complex (Ru) as relay dye, and a Cy5 derivative (Cy) or, optionally, an anthraquinone quencher (Q) were carefully analyzed using advanced distribution analysis models. Thereby, it is possible to get information on the flexibility and mobility of the chromophores which are bound to double stranded (ds) DNA. Especially the distance distribution based on the analysis of the fluorescence depolarization is an attractive approach to complement data of fluorescence decay time analysis. The distance distributions extracted from the experimental data were in excellent agreement with those determined from accessible volume (AV) simulations. Moreover, the study showed that for tc-FRET systems the combination of dyes emitting on different time scales (e.g., nanoseconds vs microseconds) is highly beneficial in the distribution analysis of time-resolved luminescence data in cases where macromolecules such as DNA are involved. Here, the short lifetimes can yield information on the rotation of the dye molecule itself and the long lifetime can give insight in the overall dynamics of the macromolecule.}, language = {en} } @article{GehneSydowDatheetal.2013, author = {Gehne, S{\"o}ren and Sydow, Karl and Dathe, Margitta and Kumke, Michael Uwe}, title = {Characterization of cell-penetrating lipopeptide micelles by spectroscopic methods}, series = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, volume = {117}, journal = {The journal of physical chemistry : B, Condensed matter, materials, surfaces, interfaces \& biophysical chemistry}, number = {46}, publisher = {American Chemical Society}, address = {Washington}, issn = {1520-6106}, doi = {10.1021/jp406053g}, pages = {14215 -- 14225}, year = {2013}, abstract = {The transport of bioactive compounds to the site of action is a great challenge. A promising approach to overcome application-related problems is the development of targeting colloidal transport systems, such as micelles which are equipped with uptake mediating moieties. Here, we investigated a set of novel lipopeptides which exhibit a surfactant-like structure due to attachment of two palmitoyl chains to the Nterminus of cationic or anionic amino acid sequences. We analyzed the association behavior of these lipopeptides by using 5(6)-carboxyfluorescein (CF)-labeled derivatives as a fluorescent probe and different spectroscopic methods such as fluorescence anisotropy and fluorescence correlation spectroscopy (FCS). The photophysical properties as well as the diffusion and rotational movements of the CF-labeled lipopeptides were exploited to determine the cmc and the size of the micelles consisting of lipopeptides. We could distinguish cationic and anionic lipopeptides by their association behavior and by studying the interactions with mouse brain capillary endothelial cells (b.end3). The cationic derivatives turned out to be very strong surfactants with a very low cmc in the micromolar range (0.5-14 mu M). The unique combination of micelle-forming property and cell-penetrating ability can pave the road for the development of a novel class of efficient drug carrier systems.}, language = {en} } @article{GrunzelPilarekSteinbruecketal.2014, author = {Grunzel, Petra and Pilarek, Maciej and Steinbrueck, Doerte and Neubauer, Antje and Brand, Eva and Kumke, Michael Uwe and Neubauer, Peter and Krause, Mirja}, title = {Mini-scale cultivation method enables expeditious plasmid production in Escherichia coli}, series = {Biotechnology journal : systems \& synthetic biology, nanobiotech, medicine}, volume = {9}, journal = {Biotechnology journal : systems \& synthetic biology, nanobiotech, medicine}, number = {1}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {1860-6768}, doi = {10.1002/biot.201300177}, pages = {128 -- 136}, year = {2014}, abstract = {The standard procedure in the lab for plasmid isolation usually involves a 2-mL, 16 h over-night cultivation in 15-mL bioreaction tubes in LB medium. This is time consuming, and not suitable for high-throughput applications. This study shows that it is possible to produce plasmid DNA (pDNA) in a 1.5-mL microcentrifuge tube with only 100 L cultivation volume in less than 7 h with a simple protocol. Compared with the standard LB cultivation for pDNA production reaching a final pDNA concentration range of 1.5-4 mu g mL(-1), a 6- to 10-fold increase in plasmid concentration (from 10 up to 25 mu g mL(-1) cultivation volume) is achieved using an optimized medium with an internal substrate delivery system (EnBase (R)). Different strains, plasmids, and the applicability of different inoculation tools (i.e. different starting ODs) were compared, demonstrating the robustness of the system. Additionally, dissolved oxygen was monitored in real time online, indicating that under optimized conditions oxygen limitation can be avoided. We developed a simple protocol with a significantly decreased procedure time, enabling simultaneous handling of more samples, while a consistent quality and a higher final pDNA concentration are ensured.}, language = {en} } @article{HaubitzDrobotTsushimaetal.2021, author = {Haubitz, Toni and Drobot, Bj{\"o}rn and Tsushima, Satoru and Steudtner, Robin and Stumpf, Thorsten and Kumke, Michael Uwe}, title = {Quenching mechanism of uranyl(VI) by chloride and bromide in aqueous and non-aqueous solutions}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {125}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {20}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.1c02487}, pages = {4380 -- 4389}, year = {2021}, abstract = {A major hindrance in utilizing uranyl(VI) luminescence as a standard analytical tool, for example, in environmental monitoring or nuclear industries, is quenching by other ions such as halide ions, which are present in many relevant matrices of uranyl(VI) speciation. Here, we demonstrate through a combination of time-resolved laser-induced fluorescence spectroscopy, transient absorption spectroscopy, and quantum chemistry that coordinating solvent molecules play a crucial role in U(VI) halide luminescence quenching. We show that our previously suggested quenching mechanism based on an internal redox reaction of the 1:2-uranyl-halide-complex holds also true for bromide-induced quenching of uranyl(VI). By adopting specific organic solvents, we were able to suppress the separation of the oxidized halide ligand X-2(center dot-) and the formed uranyl(V) into fully solvated ions, thereby "reigniting" U(VI) luminescence. Time-dependent density functional theory calculations show that quenching occurs through the outer-sphere complex of U(VI) and halide in water, while the ligand-to-metal charge transfer is strongly reduced in acetonitrile.}, language = {en} } @article{HaubitzFudickarLinkeretal.2020, author = {Haubitz, Toni and Fudickar, Werner and Linker, Torsten and Kumke, Michael Uwe}, title = {pH-sensitive fluorescence switching of pyridylanthracenes}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {124}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {52}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.0c09911}, pages = {11017 -- 11024}, year = {2020}, abstract = {9,10-substituted anthracenes are known for their useful optical properties like fluorescence, which makes them frequently used probes in sensing applications. In this article, we investigate the fundamental photophysical properties of three pyridyl-substituted variants. The nitrogen atoms in the pyridinium six-membered rings are located in the ortho-, meta-, and para-positions in relation to the anthracene core. Absorption, fluorescence, and transient absorption measurements were carried out and were complemented by theoretical calculations. We monitored the photophysics of the anthracene derivatives in chloroform and water investigating the protonated as well as their nonprotonated forms. We found that the optical properties of the nonprotonated forms are strongly determined by the anthracene chromophore, with only small differences to other 9,10-substituted anthracenes, for example diphenyl anthracene. In contrast, protonation leads to a strong decrease in fluorescence intensity and lifetime. Transient absorption measurements and theoretical calculations revealed the formation of a charge-transfer state in the protonated chromophores, where electron density is shifted from the anthracene moiety toward the protonated pyridyl substituents. While the para- and ortho-derivatives' charge transfer is still moderately fluorescent, the meta-derivative is affected much stronger and shows nearly no fluorescence. This nitrogen-atom-position-dependent sensitivity to hydronium activity makes a combination of these fluorophores very attractive for pH-sensing applications covering a broadened pH range.}, language = {en} } @article{HaubitzJohnFreyseetal.2020, author = {Haubitz, Toni and John, Leonard and Freyse, Daniel and Wessig, Pablo and Kumke, Michael Uwe}, title = {Investigating the Sulfur "Twist" on the Photophysics of DBD Dyes}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {124}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {22}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.0c01880}, pages = {4345 -- 4353}, year = {2020}, abstract = {The so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes are a new class of fluorescent dyes, with tunable photophysical properties like absorption, fluorescence lifetime, and Stokes shift. With the development of sulfur based DBDs, this dye class is extended even further for possible applications in spectroscopy and microscopy. In this paper we are investigating the basic photophysical properties and their implications for future applications for S-4-DBD as well as O-4-DBD. On the basis of time-resolved laser fluorescence spectroscopy, transient absorption spectroscopy, and UV/vis-spectroscopy, we determined the rate constants of the radiative and nonradiative deactivation processes as well as the energy of respective electronic states involved in the electronic deactivation of S-4-DBD and of O-4-DBD. For S-4-DBD we unraveled the triplet formation with intersystem crossing quantum yields of up to 80\%. By TD-DFT calculations we estimated a triplet energy of around 13500-14700 cm(-1) depending on the DBD dye and solvent. Through solvent dependent measurements, we found quadrupole moments in the range of 2 B.}, language = {en} } @article{HaubitzJohnWessigetal.2019, author = {Haubitz, Toni and John, Leonard and Wessig, Pablo and Kumke, Michael Uwe}, title = {Photophysics of Acyl- and Ester-DBD Dyes}, series = {the journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {123}, journal = {the journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {22}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.9b02973}, pages = {4717 -- 4726}, year = {2019}, abstract = {A new generation of wavelength-tunable, fluorescent dyes, so-called DBD ([1,3]dioxolo[4,5-f][1,3]benzodioxole) dyes, were developed a few years ago, and they showed great potential as probes, for example, for fluorescence microscopy. However, their photophysics is not fully explored and leaves open questions regarding their large fluorescence Stokes shifts and sensitivity to solvent conditions of differently substituted DBD dyes. To improve the understanding of the influence of the substitution pattern of the DBD dyes on their respective photophysics, transient absorption spectroscopy (TAS) was used, that is, a pump-probe experiment on the femtosecond timescale. TAS allows measurements of excited states, ground state recovery, solvent relaxation, and fluorescence properties on time scales of up to several nanoseconds. Two different DBD dye samples were investigated: aryl- and ester-substituted DBD dyes. Experiments were carried out in solvents with different polarities using different excitation energies and at different viscosities. Based on the experimental data and theoretical calculations, we were able to determine the conformational changes of the molecule due to electronic excitation and were able to investigate solvent relaxation processes for both types of DBD dyes. By generalizing the theory for quadrupole-induced solvent relaxation developed by Togashi et al., we derived quadrupole moments of both molecules in the ground and excited state. Our data showed differences in the binding of polar solvent molecules to the dyes depending on the substituent on the DBD dye. In the case of water as the solvent, an additional efficient quenching process in the electronically excited state was revealed, which was indicated by the observation of solvated electrons in the TAS signals.}, language = {en} } @article{HaubitzTsushimaSteudtneretal.2018, author = {Haubitz, Toni and Tsushima, Satoru and Steudtner, Robin and Drobot, Bj{\"o}rn and Geipel, Gerhard and Stumpf, Thorsten and Kumke, Michael Uwe}, title = {Ultrafast Transient Absorption Spectroscopy of UO(2)(2+)and [UO2Cl](+)}, series = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, volume = {122}, journal = {The journal of physical chemistry : A, Molecules, spectroscopy, kinetics, environment \& general theory}, number = {35}, publisher = {American Chemical Society}, address = {Washington}, issn = {1089-5639}, doi = {10.1021/acs.jpca.8b05567}, pages = {6970 -- 6977}, year = {2018}, abstract = {For the only water coordinated "free" uranyl (VI) aquo ion in perchlorate solution we identified and assigned several different excited states and showed that the (3)Delta state is the luminescent triplet state from transient absorption spectroscopy. With additional data from other spectroscopic methods (TRLFS, UV/vis) we generated a detailed Jablonski diagram and determined rate constants for several state transitions, like the inner conversion rate constant from the (3)Phi state to the (3)Delta state transition to be 0.35 ps(-1). In contrast to luminescence measurements, it was possible to observe the highly quenched uranyl(VI) ion in highly concentrated chloride solution by TAS and we were able to propose a dynamic quenching mechanism, where chloride complexation is followed by the charge transfer from the excited state uranyl(VI) to chloride. This proposed quenching route is supported by TD-DFT calculations.}, language = {en} } @article{HesseKlierSgarzietal.2018, author = {Hesse, Julia and Klier, Dennis Tobias and Sgarzi, Massimo and Nsubuga, Anne and Bauer, Christoph and Grenzer, Joerg and H{\"u}bner, Rene and Wislicenus, Marcus and Joshi, Tanmaya and Kumke, Michael Uwe and Stephan, Holger}, title = {Rapid Synthesis of Sub-10nm Hexagonal NaYF4-Based Upconverting Nanoparticles using Therminol((R))66}, series = {ChemistryOpen : including thesis treasury}, volume = {7}, journal = {ChemistryOpen : including thesis treasury}, number = {2}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {2191-1363}, doi = {10.1002/open.201700186}, pages = {159 -- 168}, year = {2018}, abstract = {We report a simple one-pot method for the rapid preparation of sub-10nm pure hexagonal (-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol((R))66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.}, language = {en} } @misc{HesseKlierSgarzietal.2018, author = {Hesse, Julia and Klier, Dennis Tobias and Sgarzi, Massimo and Nsubuga, Anne and Bauer, Christoph and Grenzer, J{\"o}rg and H{\"u}bner, Ren{\´e} and Wislicenus, Marcus and Joshi, Tanmaya and Kumke, Michael Uwe and Stephan, Holger}, title = {Rapid synthesis of sub-10 nm hexagonal NaYF4-based upconverting nanoparticles using Therminol® 66}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch-Naturwissenschaftliche Reihe}, number = {613}, issn = {1866-8372}, doi = {10.25932/publishup-42351}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-423515}, pages = {10}, year = {2018}, abstract = {We report a simple one-pot method for the rapid preparation of sub-10nm pure hexagonal (-phase) NaYF4-based upconverting nanoparticles (UCNPs). Using Therminol((R))66 as a co-solvent, monodisperse UCNPs could be obtained in unusually short reaction times. By varying the reaction time and reaction temperature, it was possible to control precisely the particle size and crystalline phase of the UCNPs. The upconversion (UC) luminescence properties of the nanocrystals were tuned by varying the concentrations of the dopants (Nd3+ and Yb3+ sensitizer ions and Er3+ activator ions). The size and phase-purity of the as-synthesized core and core-shell nanocrystals were assessed by using complementary transmission electron microscopy, dynamic light scattering, X-ray diffraction, and small-angle X-ray scattering studies. In-depth photophysical evaluation of the UCNPs was pursued by using steady-state and time-resolved luminescence spectroscopy. An enhancement in the UC intensity was observed if the nanocrystals, doped with optimized concentrations of lanthanide sensitizer/activator ions, were further coated with an inert/active shell. This was attributed to the suppression of surface-related luminescence quenching effects.}, language = {en} } @article{HoangHaubitzKumke2018, author = {Hoang, Hoa T. and Haubitz, Toni and Kumke, Michael Uwe}, title = {Photophysics of "Floppy" Dyadsas Potential Biomembrane Probes}, series = {Journal of fluorescence}, volume = {28}, journal = {Journal of fluorescence}, number = {5}, publisher = {Springer}, address = {New York}, issn = {1053-0509}, doi = {10.1007/s10895-018-2286-4}, pages = {1225 -- 1237}, year = {2018}, abstract = {In the study a dyad (C6 probe), constructed of two dyes with highly different hydrophobicities, was investigated by steady-state and time-resolved spectroscopic techniques in chloroform, methanol, and in phospholipid vesicles, respectively. The dyad was built on two dyes: the lipophilic benzo[a]pyrene (BaP) and the hydrophilic sulforhodamine B (SRB). The dyes were linked via a short, but flexible alkyl chain (six C-atoms). Based on their spectroscopic properties, BaP and SRB showed a very efficient non-radiative resonance energy transfer in solution. Incorporation into a lipid bilayer limited the relative flexibility (degree of freedom) between donor and acceptor and was used for the investigation of fundamental photophysical aspects (especially of FRET) as well as to elucidate the potential of the dyad to probe the interface of vesicles (or cells). The location of the two dyes in vesicles and their respective accessibility for interactions with dye-specific antibodies was investigated. Based on the alteration of the anisotropy, on the rotational correlation time as well as on the diffusion coefficient the incorporation of the C6 probe into the vesicles was evaluated. Especially the limitation in the relative movements of the two dyes was considered and used to differentiate between potential parameters, that influence the energy transfer in the dyad. Transient absorption spectroscopy (TAS) and pulsed-interleave single molecule fluorescence experiments were performed to better understand the intramolecular interactions in the dyad. Finally, in a showcase for a biosensing application of the dyads, the binding of an SRB-specific antibody was investigated when the dyad was incorporated in vesicles.}, language = {en} } @article{HoangMertensWessigetal.2018, author = {Hoang, Hoa T. and Mertens, Monique and Wessig, Pablo and Sellrie, Frank and Schenk, J{\"o}rg A. and Kumke, Michael Uwe}, title = {Antibody Binding at the Liposome-Water Interface}, series = {ACS Omega}, volume = {3}, journal = {ACS Omega}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {2470-1343}, doi = {10.1021/acsomega.8b03016}, pages = {18109 -- 18116}, year = {2018}, abstract = {Different signal amplification strategies to improve the detection sensitivity of immunoassays have been applied which utilize enzymatic reactions, nanomaterials, or liposomes. The latter are very attractive materials for signal amplification because liposomes can be loaded with a large amount of signaling molecules, leading to a high sensitivity. In addition, liposomes can be used as a cell-like "bioscaffold" to directly test recognition schemes aiming at cell-related processes. This study demonstrates an easy and fast approach to link the novel hydrophobic optical probe based on [1,3]dioxolo[4,5-f]-[1,3]benzodioxole (DBD dye mm239) with tunable optical properties to hydrophilic recognition elements (e.g., antibodies) using liposomes for signal amplification and as carrier of the hydrophobic dye. The fluorescence properties of mm239 (e.g., long fluorescence lifetime, large Stokes shift, high photostability, and high quantum yield), its high hydrophobicity for efficient anchoring in liposomes, and a maleimide bioreactive group were applied in a unique combination to build a concept for the coupling of antibodies or other protein markers to liposomes (coupling to membranes can be envisaged). The concept further allowed us to avoid multiple dye labeling of the antibody. Here, anti-TAMRA-antibody (DC7-Ab) was attached to the liposomes. In proof-of-concept, steady-state as well as time-resolved fluorescence measurements (e.g., fluorescence depolarization) in combination with single molecule detection (fluorescence correlation spectroscopy, FCS) were used to analyze the binding interaction between DC7-Ab and liposomes as well as the binding of the antigen rhodamine 6G (R6G) to the antibody. Here, the Forster resonance energy transfer (FRET) between mm239 and R6G was monitored. In addition to ensemble FRET data, single-molecule FRET (PIE-FRET) experiments using pulsed interleaved excitation were used to characterize in detail the binding on a single-molecule level to avoid averaging out effects.}, language = {en} } @article{KienzlerFlehrGehneetal.2012, author = {Kienzler, Andrea Altevogt Nee and Flehr, Roman and Gehne, S{\"o}ren and Kumke, Michael Uwe and Bannwarth, Willi}, title = {Verification and biophysical characterization of a New Three-Color Forster Resonance-Energy-Transfer (FRET) System in DNA}, series = {Helvetica chimica acta}, volume = {95}, journal = {Helvetica chimica acta}, number = {4}, publisher = {Wiley-VCH}, address = {Weinheim}, issn = {0018-019X}, doi = {10.1002/hlca.201100460}, pages = {543 -- 555}, year = {2012}, abstract = {We report on a new three-color FRET system consisting of three fluorescent dyes, i.e., of a carbostyril (=quinolin-2(1H)-one)-derived donor D, a (bathophenanthroline)ruthenium complex as a relay chromophore A1, and a Cy dye as A2 (FRET=Forster resonance-energy-transfer) (cf. Fig. 1). With their widely matching spectroscopic properties (cf. Fig. 2), the combination of these dyes yielded excellent FRET efficiencies. Furthermore, fluorescence lifetime measurements revealed that the long fluorescence lifetime of the Ru complex was transferred to the Cy dye offering the possibility to measure the whole system in a time-resolved mode. The FRET system was established on double-stranded DNA (cf. Fig. 3) but it should also be generally applicable to other biomolecules.}, language = {en} } @article{KienzlerFlehrKrameretal.2011, author = {Kienzler, Andrea and Flehr, Roman and Kramer, Rolf A. and Gehne, Soeren and Kumke, Michael Uwe and Bannwarth, Willi}, title = {Novel Three-Color FRET Tool Box for Advanced Protein and DNA Analysis}, series = {Bioconjugate chemistry}, volume = {22}, journal = {Bioconjugate chemistry}, number = {9}, publisher = {American Chemical Society}, address = {Washington}, issn = {1043-1802}, doi = {10.1021/bc2002659}, pages = {1852 -- 1863}, year = {2011}, abstract = {We report on a new three-color FRET system which we were able to verify in peptides as well as in synthetic DNA. All three chromophores could be introduced by a building block approach avoiding postsynthetic labeling. Additional features are robustness, matching spectroscopic properties, high-energy transfer, and sensitivity. The system was investigated in detail on a set of peptides as well as an array of tailored oligonucleotides. The detailed analysis of the experimental data and comparison with theoretical considerations were in excellent agreement. It is shown that in the case of polypeptides specific interaction with the fluorescence probes has to be considered. In contrast with DNA, the fluorescence probes did not show any indications of such interactions. The novel three-color FRET toolbox revealed the potential for applications studying fundamental processes of three interacting molecules in life science applications.}, language = {en} } @article{KietzkeNeherKumkeetal.2004, author = {Kietzke, Thomas and Neher, Dieter and Kumke, Michael Uwe and Montenegro, Rivelino V. D. and Landfester, Katharina and Scherf, Ullrich}, title = {A nanoparticle approach to control the phase separation in polyfluorene photovoltaic devices}, year = {2004}, abstract = {Polymer solar cell devices with nanostructured blend layers have been fabricated using single- and dual- component polymer nanospheres. Starting from an electron-donating and an electron-accepting polyfluorene derivative, PFB and F8BT, dissolved in suitable organic solvents, dispersions of solid particles with mean diameters of ca. 50 nm, containing either the pure polymer components or a mixture of PFB and F8BT in each particle, were prepared with the miniemulsion process. Photovoltaic devices based on these particles have been studied with respect to the correlation between external quantum efficiency and layer composition. It is shown that the properties of devices containing a blend of single-component PFB and F8BT particles differ significantly from those of solar cells based on blend particles, even for the same layer composition. Various factors determining the quantum efficiency in both kinds of devices are identified and discussed, taking into account the spectroscopic properties of the particles. An external quantum efficiency of ca. 4\% is measured for a device made from polymer blend nanoparticles containing PFB:F8BT at a weight ratio of 1:2 in each individual nanosphere. This is among the highest values reported so far for photovoltaic cells using this material combination}, language = {en} } @article{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale}, series = {RSC Advances : an international journal to further the chemical sciences}, journal = {RSC Advances : an international journal to further the chemical sciences}, number = {5}, publisher = {RSC Publishing}, address = {London}, issn = {2046-2069}, doi = {10.1039/C5RA11502G}, pages = {67149 -- 67156}, year = {2015}, abstract = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.}, language = {en} } @misc{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-89618}, pages = {67149 -- 67156}, year = {2015}, abstract = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.}, language = {en} } @article{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+,Er3+-co-doped NaYF4 nanomaterials}, series = {Journal of materials chemistry C ; Materials for optical and electronic devices}, journal = {Journal of materials chemistry C ; Materials for optical and electronic devices}, number = {3}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2050-7526}, doi = {10.1039/C5TC02218E}, pages = {11228 -- 11238}, year = {2015}, abstract = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.}, language = {en} } @misc{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+,Er3+-co-doped NaYF4 nanomaterials}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-89630}, pages = {11228 -- 11238}, year = {2015}, abstract = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to Tan = 700 °C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different Tan were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 °C < Tan < 600 °C the hexagonal lattice phase was dominant. For Tan < 300 °C hardly any change in the lattice phase could be deduced, whereas for Tan > 600 °C a back transfer to the α-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of Tan on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of Gfull/R is highly effected by the laser power only when the β-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 °C < Tan < 300 °C, which was not possible with the standard techniques.}, language = {en} } @article{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Analysing the effect of the crystal structure on upconversion luminescence in Yb3+, Er3+-co-doped NaYF4 nanomaterials}, series = {Journal of materials chemistry : C, Materials for optical and electronic devices}, volume = {3}, journal = {Journal of materials chemistry : C, Materials for optical and electronic devices}, number = {42}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2050-7526}, doi = {10.1039/c5tc02218e}, pages = {11228 -- 11238}, year = {2015}, abstract = {NaYF4:Yb:Er nanoparticles (UCNP) were synthesized under mild experimental conditions to obtain a pure cubic lattice. Upon annealing at different temperatures up to T-an = 700 degrees C phase transitions to the hexagonal phase and back to the cubic phase were induced. The UCNP materials obtained for different T-an were characterized with respect to the lattice phase using standard XRD and Raman spectroscopy as well as steady state and time resolved upconversion luminescence. The standard techniques showed that for the annealing temperature range 300 degrees C < T-an < 600 degrees C the hexagonal lattice phase was dominant. For T-an < 300 degrees C hardly any change in the lattice phase could be deduced, whereas for T-an > 600 degrees C a back transfer to the alpha-phase was observed. Complementarily, the luminescence upconversion properties of the annealed UCNP materials were characterized in steady state and time resolved luminescence measurements. Distinct differences in the upconversion luminescence intensity, the spectral intensity distribution and the luminescence decay kinetics were found for the cubic and hexagonal lattice phases, respectively, corroborating the results of the standard analytical techniques used. In laser power dependent measurements of the upconversion luminescence intensity it was found that the green (G1, G2) and red (R) emission of Er3+ showed different effects of T-an on the number of required photons reflecting the differences in the population routes of different energy levels involved. Furthermore, the intensity ratio of G(full)/R is highly effected by the laser power only when the beta-phase is present, whereas the G1/G2 intensity ratio is only slightly effected regardless of the crystal phase. Moreover, based on different upconversion luminescence kinetics characteristics of the cubic and hexagonal phase time-resolved area normalized emission spectra (TRANES) proved to be a very sensitive tool to monitor the phase transition between cubic and hexagonal phases. Based on the TRANES analysis it was possible to resolve the lattice phase transition in more detail for 200 degrees C < T-an < 300 degrees C, which was not possible with the standard techniques.}, language = {en} } @article{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Upconversion Luminescence Properties of NaYF4:Yb:Er Nanoparticles Codoped with Gd3+}, series = {The journal of physical chemistry : C, Nanomaterials and interfaces}, volume = {119}, journal = {The journal of physical chemistry : C, Nanomaterials and interfaces}, number = {6}, publisher = {American Chemical Society}, address = {Washington}, issn = {1932-7447}, doi = {10.1021/jp5103548}, pages = {3363 -- 3373}, year = {2015}, abstract = {The temperature-dependent upconversion luminescence of NaYF4:Yb:Er nanoparticles (UCNP) containing different contents of Gd3+ as additional dopant was characterized. The UCNP were synthesized in a hydrothermal synthesis and stabilized with citrate in order to transfer them to the water phase. Basic characterization was carried out using TEM and DLS to determine the average size of the UCNP. The XRD technique was used to investigate the crystal lattice of the UCNP. It was found that due to the presence of Gd3+, an alteration of the lattice phase from a to beta was induced which was also reflected in the observed upconversion luminescence properties of the UCNP. A detailed analysis of the upconversion luminescence spectraespecially at ultralow temperaturesrevealed the different effects of phonon coupling between the host lattice and the sensitizer (Yb3+) as well as the activator (Er3+). Furthermore, the upconversion luminescence intensity reached a maximum between 15 and 250 K depending on Gd3+ content. In comparison to the very complex temperature behavior of the upconversion luminescence in the temperature range <273 K, the luminescence intensity ratio of H-2(11/2)-> I-4(15/2) to S-4(3/2)-> I-4(15/2) (R = G1/G2) in a higher temperature range can be described by an Arrhenius-type equation.}, language = {en} } @article{KlierKumke2015, author = {Klier, Dennis Tobias and Kumke, Michael Uwe}, title = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale}, series = {RSC Advances}, volume = {5}, journal = {RSC Advances}, number = {82}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {2046-2069}, doi = {10.1039/c5ra11502g}, pages = {67149 -- 67156}, year = {2015}, abstract = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure beta crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.}, language = {en} } @article{KramerFlehrLayetal.2009, author = {Kramer, Rolf A. and Flehr, Roman and Lay, Myriam and Kumke, Michael Uwe and Bannwarth, Willi}, title = {Comparative studies of different quinoline derivatives as donors in fluorescence-resonance-energy-transfer (FRET) : systems in combination with a (Bathophenanthroline)ruthenium(II) complex as acceptor}, issn = {0018-019X}, doi = {10.1002/hlca.200900235}, year = {2009}, language = {en} } @article{KramerKainmuellerFlehretal.2008, author = {Kramer, Rolf A. and Kainm{\"u}ller, Eva K. and Flehr, Roman and Kumke, Michael Uwe and Bannwarth, Willi}, title = {Quenching of the long-lived Ru(II)bathophenanthroline luminescence for the detection of supramolecular interactions}, year = {2008}, language = {en} } @article{KukeMarmodeeEidneretal.2010, author = {Kuke, S. and Marmodee, Bettina and Eidner, Sascha and Schilde, Uwe and Kumke, Michael Uwe}, title = {Intramolecular deactivation processes in complexes of salicylic acid or glycolic acid with Eu(III)}, issn = {0584-8539}, year = {2010}, abstract = {The complexation of Eu(III) by 2-hydroxy benzoic acid (2HB) or glycolic acid (GL) was investigated using steady- state and time-resolved laser spectroscopy. Experiments were carried out in H2O as well as in D2O in the temperature range of View the MathML source. The Eu(III) luminescence spectra and luminescence decay times were evaluated with respect to the temperature dependence of (i) the luminescence decay time ;, (ii) the energy of the View the MathML source transition, (iii) the width of the View the MathML source transition, and (iv) the asymmetry ratio calculated from the luminescence intensities of the View the MathML source and View the MathML source transition, respectively. The differences in ligand-related luminescence quenching are discussed. Based on the temperature dependence of the luminescence decay times an activation energy for the ligand-specific non-radiative deactivation in Eu(III)-2HB or Eu(III)-GL complexes was determined. It is stressed that ligand-specific quenching processes (other than OH quenching induced by water molecules) need to be determined and considered in detail, in order to extract speciation- relevant information from luminescence data (e.g., estimation of the number of water molecules nH2O in the first coordination sphere of Eu(III)). In case of 2HB, conclusions drawn from the evaluation of the Eu(III) luminescence are compared with results of a X-ray structure analysis.}, language = {en} } @phdthesis{Kumke2005, author = {Kumke, Michael Uwe}, title = {Huminstoffe und organische Modellliganden und ihre Wechselwirkung mit Metallionen und polyzyklischen aromatischen Kohlenwasserstoffen}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-6066}, school = {Universit{\"a}t Potsdam}, year = {2005}, abstract = {Immobilisierung bzw. Mobilisierung und Transport von Schadstoffen in der Umwelt, besonders in den Kompartimenten Boden und Wasser, sind von fundamentaler Bedeutung f{\"u}r unser ({\"U}ber)Leben auf der Erde. Einer der Hauptreaktionspartner f{\"u}r organische und anorganische Schadstoffe (Xenobiotika) in der Umwelt sind Huminstoffe (HS). HS sind Abbauprodukte pflanzlichen und tierischen Gewebes, die durch eine Kombination von chemischen und biologischen Ab- und Umbauprozessen entstehen. Bedingt durch ihre Genese stellen HS außerordentlich heterogene Stoffsysteme dar, die eine Palette von verschiedenartigen Wechselwirkungen mit Schadstoffen zeigen. Die Untersuchung der fundamentalen Wechselwirkungsmechanismen stellt ebenso wie deren quantitative Beschreibung h{\"o}chste Anforderungen an die Untersuchungsmethoden. Zur qualitativen und quantitativen Charakterisierung der Wechselwirkungen zwischen HS und Xenobiotika werden demnach analytische Methoden ben{\"o}tigt, die bei der Untersuchung von extrem heterogenen Systemen aussagekr{\"a}ftige Daten zu liefern verm{\"o}gen. Besonders spektroskopische Verfahren, wie z.B. lumineszenz-basierte Verfahren, besitzen neben der hervorragenden Selektivit{\"a}t und Sensitivit{\"a}t, auch eine Multidimensionalit{\"a}t (bei der Lumineszenz sind es die Beobachtungsgr{\"o}ßen Intensit{\"a}t IF, Anregungswellenl{\"a}nge lex, Emissionswellenl{\"a}nge lem und Fluoreszenzabklingzeit tF), die es gestattet, auch heterogene Systeme wie HS direkt zu untersuchen. Zur Charakterisierung k{\"o}nnen sowohl die intrinsischen Fluoreszenzeigenschaften der HS als auch die von speziell eingef{\"u}hrten Lumineszenzsonden verwendet werden. In beiden F{\"a}llen werden die zu Grunde liegenden fundamentalen Konzepte der Wechselwirkungen von HS mit Xenobiotika untersucht und charakterisiert. F{\"u}r die intrinsische Fluoreszenz der HS konnte gezeigt werden, dass neben molekularen Strukturen besonders die Verkn{\"u}pfung der Fluorophore im Gesamt-HS-Molek{\"u}l von Bedeutung ist. Konformative Freiheit und die Nachbarschaft zu als Energieakzeptor fungierenden HS-eigenen Gruppen sind wichtige Komponenten f{\"u}r die Charakteristik der HS-Fluoreszenz. Die L{\"o}schung der intrinsischen Fluoreszenz durch Metallkomplexierung ist demnach auch das Resultat der ver{\"a}nderten konformativen Freiheit der HS durch die gebundenen Metallionen. Es zeigte sich, dass abh{\"a}ngig vom Metallion sowohl L{\"o}schung als auch Verst{\"a}rkung der intrinsischen HS-Fluoreszenz beobachtet werden kann. Als extrinsische Lumineszenzsonden mit wohl-charakterisierten photophysikalischen Eigenschaften wurden polyzyklische aromatische Kohlenwasserstoffe und Lanthanoid-Ionen eingesetzt. Durch Untersuchungen bei sehr niedrigen Temperaturen (10 K) konnte erstmals die Mikroumgebung von an HS gebundenen hydrophoben Xenobiotika untersucht werden. Im Vergleich mit Raumtemperaturexperimenten konnte gezeigt werden, dass hydrophobe Xenobiotika an HS-gebunden in einer Mikroumgebung, die in ihrer Polarit{\"a}t analog zu kurzkettigen Alkoholen ist, vorliegen. F{\"u}r den Fall der Metallkomplexierung wurden Energietransferprozesse zwischen HS und Lanthanoidionen bzw. zwischen verschiedenen, gebundenen Lanthanoidionen untersucht. Basierend auf diesen Messungen k{\"o}nnen Aussagen {\"u}ber die beteiligten elektronischen Zust{\"a}nde der HS einerseits und Entfernungen von Metallbindungsstellen in HS selbst angeben werden. Es ist dabei zu beachten, dass die Experimente in L{\"o}sung bei realen Konzentrationen durchgef{\"u}hrt wurden. Aus Messung der Energietransferraten k{\"o}nnen direkte Aussagen {\"u}ber Konformations{\"a}nderungen bzw. Aggregationsprozesse von HS abgeleitet werden.}, subject = {Fluoreszenz}, language = {de} } @article{KumkeDoscheFlehretal.2006, author = {Kumke, Michael Uwe and Dosche, Carsten and Flehr, Roman and Trowitzsch-Kienast, Wolfram and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Spectroscopic characterization of the artificial siderophore pyridinochelin}, issn = {0939-5075}, year = {2006}, language = {en} } @misc{KumkeEidner2005, author = {Kumke, Michael Uwe and Eidner, Sascha}, title = {Fluorescence and energy transfer processes of humic substances and related model compounds in terbium complexes}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12255}, year = {2005}, abstract = {The fluorescence properties and the fluorescence quenching by Tb3+ of substituted benzoic acid were investigated in solution at different pH. The substituted benzoic acids were used as simple model compounds for chromophores present in humic substances (HS). It is shown that the fluorescence properties of the model compounds resemble fluorescence of HS quite well. A major factor determining the fluorescence of model compounds are proton transfer reactions in the electronically excited state. It is intriguing that the fluorescence of the model compounds was almost not quenched by Tb3+ while the HS fluorescence was decreased very effectively. From our results we concluded that proton transfer reactions as well as conformational reorientation processes play an important role in the fluorescence of HS. The luminescence of bound Tb3+ was sensitized by an energy transfer step upon excitation of the model compounds and of HS, respectively. For HS the observed sensitization was dependent on its origin indicating differences 1) in the connection between chromophores and binding sites and 2) in the energy levels of the chromophore triplet states. Hence, the observed sensitization of the Tb3+ luminescence could be useful to characterize structural differences of HS in solution. Interlanthanide energy transfer between Tb3+ and Nd3+ was used to determine the average distance R between both ions using the well-known formalism of luminescence resonance energy transfer. R was dependent on the origin of the HS reflecting the difference in structure. The value of Rmin seemed to be a unique feature of the HS. It was further found that upon variation of the pH R also changed. This demonstrates that the measurement of interlanthanide energy transfer can be used as a direct method to monitor conformational changes in HS.}, language = {en} } @article{KumkeEidnerKrueger2005, author = {Kumke, Michael Uwe and Eidner, Sascha and Kr{\"u}ger, Tobias}, title = {Fluorescence quenching and luminescence sensitization in complexes of Tb3+ and Eu3+ with humic substances}, year = {2005}, abstract = {Intrinsic fluorescence quenching of humic substances (HS) and the sensitization of Ln(3+) luminescence (Ln3+ Tb3+, Eu3+) in HS complexes were investigated. Both measurements yielded complementary information on the complexation of metals by HS. Large differences between fulvic acids(FA)and humic acids (HA) were found. From time-resolved luminescence measurements it is concluded that a combination of energy transfer and energy back transfer between HS and Ln(3+) is responsible for the observed luminescence decay characteristics. In the case of Eu3+, an additional participation of charge-transfer states is suggested. A new concept for the evaluation of the sensitized luminescence decays of Ln(3+) was adapted}, language = {en} } @misc{KumkeFrimmel2002, author = {Kumke, Michael Uwe and Frimmel, Fritz Hartmann}, title = {Stationary and time-resolved fluorescence for humic substances characterization}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-12353}, year = {2002}, abstract = {Steady-state and time-resolved fluorescence methods were applied to investigate the fluorescence properties of humic substances of different origins. Using standard 2D emission and total luminescence spectra, fluorescence maxima, the width of the fluorescence band and a relative fluorescence quantum efficiency were determined. Different trends for fulvic acids and humic acids were observed indicating differences in the heterogeneity of the sample fractions. The complexity of the fluorescence decay of humic substances is discussed and compared to simple model compounds. The effect of oxidation of humic substances on their fluorescence properties is discussed as well.}, language = {en} } @misc{KumkeKlier2015, author = {Kumke, Michael Uwe and Klier, Dennis Tobias}, title = {Upconversion NaYF4:Yb:Er nanoparticles co-doped with Gd3+ and Nd3+ for thermometry on the nanoscale}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-102677}, pages = {67149 -- 67156}, year = {2015}, abstract = {In the present work, the upconversion luminescence properties of oleic acid capped NaYF4:Gd3+:Yb3+:Er3+ upconversion nanoparticles (UCNP) with pure β crystal phase and Nd3+ ions as an additional sensitizer were studied in the temperature range of 288 K < T < 328 K. The results of this study showed that the complex interplay of different mechanisms and effects, causing the special temperature behavior of the UCNP can be developed into thermometry on the nanoscale, e.g. to be applied in biological systems on a cellular level. The performance was improved by the use of Nd3+ as an additional dopant utilizing the cascade sensitization mechanism in tri-doped UCNP.}, language = {en} } @article{KumkeLoehmannsroeben2009, author = {Kumke, Michael Uwe and L{\"o}hmannsr{\"o}ben, Hans-Gerd}, title = {Introduction to fluorescence spectroscopy}, year = {2009}, language = {en} } @article{KumkeOhlenbuschFrimmel2000, author = {Kumke, Michael Uwe and Ohlenbusch, G. and Frimmel, Fritz Hartmann}, title = {Sorption of phenols to dissolved organic matter investigaded by solid phase micriextrakrion}, year = {2000}, language = {en} } @article{KumkeSpechtFrimmel2000, author = {Kumke, Michael Uwe and Specht, C. H. and Frimmel, Fritz Hartmann}, title = {Characterization of NOM adsorption to clay minerals by sizs exclusion chromatography}, year = {2000}, language = {en} } @article{KumkeZwienerAbbtBraunetal.2000, author = {Kumke, Michael Uwe and Zwiener, Christian and Abbt-Braun, Gudrun and Frimmel, Fritz Hartmann}, title = {Spectroscopic characterization of fulvic acid fractions of a contaminated groundwater}, year = {2000}, language = {en} } @article{KupstatKumkeHildebrandt2011, author = {Kupstat, Annette and Kumke, Michael Uwe and Hildebrandt, Niko}, title = {Toward sensitive, quantitative point-of-care testing (POCT) of protein markers miniaturization of a homogeneous time-resolved fluoroimmunoassay for prostate-specific antigen detection}, series = {The analyst : the analytical journal of the Royal Society of Chemistry}, volume = {136}, journal = {The analyst : the analytical journal of the Royal Society of Chemistry}, number = {5}, publisher = {Royal Society of Chemistry}, address = {Cambridge}, issn = {0003-2654}, doi = {10.1039/c0an00684j}, pages = {1029 -- 1035}, year = {2011}, abstract = {Point-of-care testing (POCT) systems which allow for a sensitive, quantitative detection of protein markers are extremely useful for the early detection and therapy progress monitoring of cancer. However, currently commercially available POCT devices are mainly limited to the qualitative detection of protein markers. In this study we demonstrate the successive miniaturization of a sensitive and fast assay for the quantitative detection of prostate-specific antigen (PSA) using a well established and clinically approved homogeneous time-resolved fluoroimmunoassay technology (TRACE (R)) on a commercial plate-reader system (KRYPTOR (R)). Regarding the initial requirements for the development of POCT devices we applied a 30-fold assay volume reduction (150 mu L to 5 mu L) to achieve a reasonable lab-on-a-chip volume and a 24-fold and 120-fold excitation pulse energy reduction to achieve reasonable pulse energies for low-cost miniature excitation sources. Due to highly efficient optimization of key POCT parameters our miniaturized PSA assay achieved a 30\% increased sensitivity and a 2-fold improved limit of detection compared to the standard plate-reader method. Our results demonstrate the successful implementation of key parameters for a significant miniaturization and for cost reduction in the clinically approved KRYPTOR (R) platform for protein detection. The technological alterations required are easy-to-implement and can be immediately adapted for more than 30 diagnostic protein markers already available for the KRYPTOR (R) platform. These features strongly recommend our assay format to be utilized in innovative, sensitive, quantitative POCT of protein markers.}, language = {en} } @article{KupstatRitschelKumke2011, author = {Kupstat, Annette and Ritschel, Thomas and Kumke, Michael Uwe}, title = {Oxazine Dye-Conjugated DNA Oligonucleotides Forster Resonance Energy Transfer in View of Molecular Dye-DNA Interactions}, series = {Bioconjugate chemistry}, volume = {22}, journal = {Bioconjugate chemistry}, number = {12}, publisher = {American Chemical Society}, address = {Washington}, issn = {1043-1802}, doi = {10.1021/bc200379y}, pages = {2546 -- 2557}, year = {2011}, abstract = {In this work, the photophysical properties of two oxazine dyes (ATTO 610 and ATTO 680) covalently attached via a C6-amino linker to the 5'-end of short single-stranded as well as double-stranded DNA (ssDNA and dsDNA, respectively) of different lengths were investigated. The two oxazine dyes were chosen because of the excellent spectral overlap, the high extinction coefficients, and the high fluorescence quantum yield of ATTO 610, making them an attractive Forster resonance energy transfer (FRET) pair for bioanalytical applications in the far-red spectral range. To identify possible molecular dye-DNA interactions that cause photophysical alterations, we performed a detailed spectroscopic study, including time-resolved fluorescence anisotropy and fluorescence correlation spectroscopy measurements. As an effect of the DNA conjugation, the absorption and fluorescence maxima of both dyes were bathochromically shifted and the fluorescence decay times were increased. Moreover, the absorption of conjugated ATTO 610 was spectrally broadened, and a dual fluorescence emission was observed. Steric interactions with ssDNA as well as dsDNA were found for both dyes. The dye-DNA interactions were strengthened from ssDNA to dsDNA conjugates, pointing toward interactions with specific dsDNA domains (such as the top of the double helix). Although these interactions partially blocked the dye-linker rotation, a free (unhindered) rotational mobility of at least one dye facilitated the appropriate alignment of the transition dipole moments in doubly labeled ATTO 610/ATTO 680-dsDNA conjugates for the performance of successful FRET. Considering the high linker flexibility for the determination of the donor-acceptor distances, good accordance between theoretical and experimental FRET parameters was obtained. The considerably large Forster distance of similar to 7 nm recommends the application of this FRET pair not only for the detection of binding reactions between nucleic acids in living cells but also for monitoring interactions of larger biomolecules such as proteins.}, language = {en} } @article{LippoldEidnerKumkeetal.2017, author = {Lippold, Holger and Eidner, Sascha and Kumke, Michael Uwe and Lippmann-Pipke, Johanna}, title = {Dynamics of metal-humate complexation equilibria as revealed by isotope exchange studies - a matter of concentration and time}, series = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society}, volume = {197}, journal = {Geochimica et cosmochimica acta : journal of the Geochemical Society and the Meteoritical Society}, publisher = {Elsevier}, address = {Oxford}, issn = {0016-7037}, doi = {10.1016/j.gca.2016.10.019}, pages = {62 -- 70}, year = {2017}, abstract = {Complexation with dissolved humic matter can be crucial in controlling the mobility of toxic or radioactive contaminant metals. For speciation and transport modelling, a dynamic equilibrium process is commonly assumed, where association and dissociation run permanently. This is, however, questionable in view of reported observations of a growing resistance to dissociation over time. In this study, the isotope exchange principle was employed to gain direct insight into the dynamics of the complexation equilibrium, including kinetic inertisation phenomena. Terbium(III), an analogue of trivalent actinides, was used as a representative of higher-valent metals. Isotherms of binding to (flocculated) humic acid, determined by means of Tb-160 as a radiotracer, were found to be identical regardless of whether the radioisotope was introduced together with the bulk of stable Tb-159 or subsequently after pre-equilibration for up to 3 months. Consequently, there is a permanent exchange of free and humic-bound Tb since all available binding sites are occupied in the plateau region of the isotherm. The existence of a dynamic equilibrium was thus evidenced. There was no indication of an inertisation under these experimental conditions. If the small amount of Tb-160 was introduced prior to saturation with Tb-159, the expected partial desorption of Tb-160 occurred at much lower rates than observed for the equilibration process in the reverse procedure. In addition, the rates decreased with time of pre-equilibration. Inertisation phenomena are thus confined to the stronger sites of humic molecules (occupied at low metal concentrations). Analysing the time-dependent course of isotope exchange according to first-order kinetics indicated that up to 3 years are needed to attain equilibrium. Since, however, metal-humic interaction remains reversible, exchange of metals between humic carriers and mineral surfaces cannot be neglected on the long time scale to be considered in predictive transport models.}, language = {en} } @article{LippoldEidnerKumkeetal.2012, author = {Lippold, Holger and Eidner, Sascha and Kumke, Michael Uwe and Lippmann-Pipke, Johanna}, title = {Diffusion, degradation or on-site stabilisation - identifying causes of kinetic processes involved in metal-humate complexation}, series = {Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry}, volume = {27}, journal = {Applied geochemistry : journal of the International Association of Geochemistry and Cosmochemistry}, number = {1}, publisher = {Elsevier}, address = {Oxford}, issn = {0883-2927}, doi = {10.1016/j.apgeochem.2011.11.001}, pages = {250 -- 256}, year = {2012}, abstract = {The applicability of equilibrium models for humic-bound transport of toxic or radioactive metals is affected by kinetic processes leading to an increasing inertness of metal-humic complexes. The chemical background is not yet understood. It is widely believed that bound metals undergo an in-diffusion process within the humic colloids, changing from weaker to stronger binding sites. This work is focussed on the competition effect of Al(III) on complexation of Tb(III) or Eu(III) as analogues of trivalent actinides. By using ion exchange and spectroscopic methods, their bound fractions were determined for solutions of Al and humic acid that had been pre-equilibrated for different periods of time. Whilst the amount of bound Al remained unchanged, its blocking effect was found to increase over a time frame of 2 days, which corresponds to the kinetics of the increase in complex inertness reported in most pertinent studies. Thus, the derived "diffusion theory'' turned out to be inapplicable, since it cannot explain an increase in competition for the "initial'' sites. A delayed degradation of polynuclear species (as found for Fe) does not occur. Consequently, the temporal changes must be based on structural rearrangements in the vicinity of bound Al, complicating the exchange or access. Time-dependent studies by laser fluorescence spectroscopy (steady-state and time-resolved) yielded evidence of substantial alterations, which were, however, immediately induced and did not show any significant trend on the time scale of interest, suggesting that the stabilisation process is based on comparatively moderate changes.}, language = {en} } @article{LuschtinetzDoscheKumke2009, author = {Luschtinetz, Franziska and Dosche, Carsten and Kumke, Michael Uwe}, title = {Influence of streptavidin on the absorption and fluorescence properties of cyanine dyes}, issn = {1043-1802}, doi = {10.1021/Bc800497v}, year = {2009}, abstract = {Cyanine dyes have become widely used fluorescence labels in clinical and biological chemistry. In particular, cyanine dyes with excitation wavelengths lambda(ex) > 600 nm are often used in biological applications. However, aggregation behavior and matrix effects on cyanine fluorescence are not fully understood yet and interfere with the data interpretation. In this study, we analyzed the spectroscopic characteristics of a model system consisting of the biotinylated cyanine dyes DY-635 and DY-647 and their streptavidin conjugates. On the basis of the spectroscopic data, the interaction processes between cyanine dye molecules and proteins are discussed. Binding to streptavidin had a significant influence on both fluorescence and anisotropy decays of the cyanine dyes investigated. In particular, the fluorescence anisotropy was significantly altered, making it a promising detection parameter for bioanalytical applications in connection with the cyanine dyes used in the present study. In order to evaluate the time-resolved anisotropy, the introduction of a sophisticated kinetic model was required to describe the contributions from different fluorescing species properly. The rotational motion of streptavidin-bound dyes was analyzed using the associated anisotropy model, which allowed discrimination between contributions from different microenvironments. The anisotropy decay times increased by a factor of up to 20 due to protein binding.}, language = {en} } @misc{LopezdeGuerenuBastianWessigetal.2019, author = {L{\´o}pez de Guere{\~n}u, Anna and Bastian, Philipp and Wessig, Pablo and John, Leonard and Kumke, Michael Uwe}, title = {Energy transfer between tm-doped upconverting nanoparticles and a small organic dye with large stokes shift}, series = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, journal = {Postprints der Universit{\"a}t Potsdam : Mathematisch Naturwissenschaftliche Reihe}, number = {961}, issn = {1866-8372}, doi = {10.25932/publishup-47224}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-472240}, pages = {19}, year = {2019}, abstract = {Lanthanide-doped upconverting nanoparticles (UCNP) are being extensively studied for bioapplications due to their unique photoluminescence properties and low toxicity. Interest in RET applications involving UCNP is also increasing, but due to factors such as large sizes, ion emission distributions within the particles, and complicated energy transfer processes within the UCNP, there are still many questions to be answered. In this study, four types of core and core-shell NaYF4-based UCNP co-doped with Yb3+ and Tm3+ as sensitizer and activator, respectively, were investigated as donors for the Methyl 5-(8-decanoylbenzo[1,2-d:4,5-d ']bis([1,3]dioxole)-4-yl)-5-oxopentanoate (DBD-6) dye. The possibility of resonance energy transfer (RET) between UCNP and the DBD-6 attached to their surface was demonstrated based on the comparison of luminescence intensities, band ratios, and decay kinetics. The architecture of UCNP influenced both the luminescence properties and the energy transfer to the dye: UCNP with an inert shell were the brightest, but their RET efficiency was the lowest (17\%). Nanoparticles with Tm3+ only in the shell have revealed the highest RET efficiencies (up to 51\%) despite the compromised luminescence due to surface quenching.}, language = {en} } @article{LopezdeGuerenuBastianWessigetal.2019, author = {L{\´o}pez de Guere{\~n}u, Anna and Bastian, Philipp and Wessig, Pablo and John, Leonard and Kumke, Michael Uwe}, title = {Energy Transfer between Tm-Doped Upconverting Nanoparticles and a Small Organic Dye with Large Stokes Shift}, series = {Biosensors : open access journal}, volume = {9}, journal = {Biosensors : open access journal}, number = {1}, publisher = {MDPI}, address = {Basel}, issn = {2079-6374}, doi = {10.3390/bios9010009}, pages = {17}, year = {2019}, abstract = {Lanthanide-doped upconverting nanoparticles (UCNP) are being extensively studied for bioapplications due to their unique photoluminescence properties and low toxicity. Interest in RET applications involving UCNP is also increasing, but due to factors such as large sizes, ion emission distributions within the particles, and complicated energy transfer processes within the UCNP, there are still many questions to be answered. In this study, four types of core and core-shell NaYF4-based UCNP co-doped with Yb3+ and Tm3+ as sensitizer and activator, respectively, were investigated as donors for the Methyl 5-(8-decanoylbenzo[1,2-d:4,5-d ']bis([1,3]dioxole)-4-yl)-5-oxopentanoate (DBD-6) dye. The possibility of resonance energy transfer (RET) between UCNP and the DBD-6 attached to their surface was demonstrated based on the comparison of luminescence intensities, band ratios, and decay kinetics. The architecture of UCNP influenced both the luminescence properties and the energy transfer to the dye: UCNP with an inert shell were the brightest, but their RET efficiency was the lowest (17\%). Nanoparticles with Tm3+ only in the shell have revealed the highest RET efficiencies (up to 51\%) despite the compromised luminescence due to surface quenching.}, language = {en} } @article{LopezdeGuerenuKurganovaKlierHaubitzetal.2022, author = {L{\´o}pez de Guere{\~n}u Kurganova, Anna and Klier, Dennis Tobias and Haubitz, Toni and Kumke, Michael Uwe}, title = {Influence of Gd3+ doping concentration on the properties of Na(Y,Gd)F-4}, series = {Photochemical \& photobiological sciences / European Society for Photobiology}, volume = {21}, journal = {Photochemical \& photobiological sciences / European Society for Photobiology}, number = {2}, publisher = {Springer}, address = {Heidelberg}, issn = {1474-905X}, doi = {10.1007/s43630-021-00161-4}, pages = {235 -- 245}, year = {2022}, abstract = {We present a systematic study on the properties of Na(Y,Gd)F-4-based upconverting nanoparticles (UCNP) doped with 18\% Yb3+, 2\% Tm3+, and the influence of Gd3+ (10-50 mol\% Gd3+). UCNP were synthesized via the solvothermal method and had a range of diameters within 13 and 50 nm. Structural and photophysical changes were monitored for the UCNP samples after a 24-month incubation period in dry phase and further redispersion. Structural characterization was performed by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) as well as dynamic light scattering (DLS), and the upconversion luminescence (UCL) studies were executed at various temperatures (from 4 to 295 K) using time-resolved and steady-state spectroscopy. An increase in the hexagonal lattice phase with the increase of Gd3+ content was found, although the cubic phase was prevalent in most samples. The Tm3+-luminescence intensity as well as the Tm3+-luminescence decay times peaked at the Gd3+ concentration of 30 mol\%. Although the general upconverting luminescence properties of the nanoparticles were preserved, the 24-month incubation period lead to irreversible agglomeration of the UCNP and changes in luminescence band ratios and lifetimes.}, language = {en} } @misc{LoehmannsroebenKantorKumkeetal.2005, author = {L{\"o}hmannsr{\"o}ben, Hans-Gerd and Kantor, Zoltan and Kumke, Michael Uwe and Schm{\"a}lzlin, Elmar and Reich, Oliver}, title = {OPQS - optische Prozess- und Qualit{\"a}ts-Sensorik}, url = {http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-13205}, year = {2005}, abstract = {Im vorliegenden Beitrag wird an Hand dreier Beispiele der Einsatz von optischer Sensorik zur Produktcharakterisierung dargestellt, n{\"a}mlich Untersuchungen zum O2-Gehalt in Fruchts{\"a}ften, zur Isotopiesignatur von CO2 in Mineralw{\"a}ssern und zu Lichtstreueigenschaften eines Sonnenschutzmittels. Inhalt: Bestimmung von O2 mit Lumineszenzsonden Isotopenselektive Bestimmung von CO2 mit TDLAS Optische Charakterisierung stark streuender Materialien mit Photonendichtewellen}, language = {de} }