TY - JOUR A1 - Resch-Genger, Ute A1 - Grabolle, Markus A1 - Starke, M. T1 - Highly fluorescent dye-nanoclay hybrid materials made from different dye classes N2 - Nanoclays like laponites, which are commercially avaible in large quantities for a very moderate price, provide a facile solubilization strategy for hydrophobic dyes without the need for chemical functionalization and can act as a carrier for a high number of dye molecules. This does not require reactive dyes, amplifies fluorescence signals from individual emitters due to the high number of dyes molecules per laponite disk, and renders hydrophobic emitters applicable in aqueous environments. Aiming at the rational design of bright dye-loaded nanoclays as a new class of fluorescent reporters for bioanalysis and material sciences and the identification of dye structure−property relationships, we screened a series of commercial fluorescent dyes, differing in dye class, charge, and character of the optical transitions involved, and studied the changes of their optical properties caused by clay adsorption at different dye loading concentrations. Upon the basis of our dye loading density-dependent absorption and fluorescence measurements with S2105 and Lumogen F Yellow 083, we could identify two promising dye−nanoclay hybrid materials that reveal high fluorescence quantum yields of the nanoclay-adsorbed dyes of at least 0.20 and low dye self-quenching even at high dye-loading densities of up to 50 dye molecules per laponite platelet. KW - nanoclay KW - laponite KW - fluorescence KW - organic dye KW - carrier system KW - fluorescent reporter KW - screening PY - 2016 U6 - https://doi.org/10.1021/acs.langmuir.5b04297 SN - 0743-7463 VL - 2016 IS - 32 SP - 3506 EP - 3513 PB - Amer Chemical SOC CY - Washington, DC, USA AN - OPUS4-36511 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Brömme, T. A1 - Schmitz, C. A1 - Oprych, D. A1 - Wenda, A. A1 - Strehmel, V. A1 - Grabolle, Markus A1 - Resch-Genger, Ute A1 - Ernst, S. A1 - Reiner, K. A1 - Keil, D. A1 - Lüs, P. A1 - Baumann, H. A1 - Strehmel, B. T1 - Digital imaging of lithographic materials by radical photopolymerization and photonic baking with NIR diode lasers N2 - Photo-initiated cross-linking of multifunctional acrylic esters in polymeric binders was investigated based on digital imaging using the Computer-to-Plate (CtP) technology applying laser exposure in the near-infrared (NIR). Generation of initiating radicals occurs by electron transfer from the excited state of the NIR-sensitizer to the radical generator, an onium salt. Iodonium salts derived from several borates and those with the bis(trifluoromethylsulfonyl)imide anion resulted in lithographic materials with high sensitivity. Photo-induced electron transfer plays a major function to generate initiating radicals by a sensitized mechanism but thermal events also influence sensitivity of the coating. Internal conversion was the major deactivation pathway while a certain fraction of NIR-dye fluorescence was also available. A line shape focused laser system with emission in the NIR was successfully used to bake the materials. KW - Iodonium KW - Near-infrared laser KW - Photonic baking KW - Photophysics KW - Photopolymer PY - 2016 U6 - https://doi.org/10.1002/ceat.201500453 SN - 0930-7516 SN - 1521-4125 VL - 39 IS - 1 SP - 13 EP - 25 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-35303 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Otto, S. A1 - Grabolle, Markus A1 - Förster, C. A1 - Kreitner, C. A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - [Cr(ddpd)2]3+: A molecular, water-soluble, highly NIR-emissive ruby analogue N2 - Bright, long-lived emission from first-row transition-metal complexes is very challenging to achieve. Herein, we present a new strategy relying on the rational tuning of energy levels. With the aid of the large N-Cr-N bite angle of the tridentate ligand ddpd (N,N′-dimethyl-N,N′-dipyridine-2-ylpyridine-2,6-diamine) and its strong σ-donating capabilities, a very large ligand-field splitting could be introduced in the chromium(III) complex [Cr(ddpd)2]3+, that shifts the deactivating and photoreactive 4T2 state well above the emitting 2E state. Prevention of back-intersystem crossing from the 2E to the 4T2 state enables exceptionally high near-infrared phosphorescence quantum yields and lifetimes for this 3d metal complex. The complex [Cr(ddpd)2](BF4)3 is highly water-soluble and very stable towards thermal and photo-induced substitution reactions and can be used for fluorescence intensity- and lifetime-based oxygen sensing in the NIR. KW - Chromium complexes KW - Intersystem crossing KW - Ligand-field splitting KW - NIR luminescence KW - Photophysics PY - 2015 U6 - https://doi.org/10.1002/anie.201504894 SN - 1433-7851 SN - 1521-3773 SN - 0570-0833 VL - 54 IS - 39 SP - 11572 EP - 11576 PB - Wiley-VCH CY - Weinheim AN - OPUS4-35084 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kreitner, C. A1 - Grabolle, Markus A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - Dual emission and excited-state mixed-valence in a quasi-symmetric dinuclear Ru-Ru complex N2 - The synthesis and characterization of the new dinuclear dipeptide [(EtOOC-tpy)Ru(tpy-NHCO-tpy)Ru(tpy-NHCOCH3)]4+ 34+ of the bis(terpyridine)ruthenium amino acid [(HOOC-tpy)Ru(tpy-NH2)]2+ 12+ are described, and the properties of the dipeptide are compared to those of the mononuclear complex [(EtOOC-tpy)Ru(tpy-NHCOCH3)]2+ 42+ carrying the same functional groups. 34+ is designed to serve a high electronic similarity of the two ruthenium sites despite the intrinsic asymmetry arising from the amide bridge. This is confirmed via UV–vis absorption and NMR spectroscopy as well as cyclic voltammetry. 42+ and 34+ are emissive at room temperature, as expected. Moreover, 34+ exhibits dual emission from two different triplet states with different energies and lifetimes at room temperature. This is ascribed to the presence of a unique thermal equilibrium between coexisting [RuII(tpy-NHCO-tpy·–)RuIII] and [RuIII(tpy-NHCO-tpy·–)RuII] states leading to an unprecedented excited-state RuIIRuIII mixed-valent system via the radical anion bridge tpy-NHCO-tpy·–. The mixed-valent cation 35+, on the other hand, shows no measurable interaction of the RuIIRuIII centers via the neutral bridge tpy-NHCO-tpy (Robin–Day class I). Reduction of 34+ to the radical cation 33+ by decamethylcobaltocene is bridge-centered as evidenced by rapid-freeze electron paramagnetic resonance spectroscopy. Interestingly, all attempts to observe 33+ via NMR and UV–vis absorption spectroscopy only led to the detection of the diamagnetic complex 3-H3+ in which the bridging amide is deprotonated. Hence 3-H3+ (and 4-H+) appear to reduce protons to dihydrogen. The ease of single and double deprotonation of 42+ and 34+ to 4-H+, 3-H3+, and 3-2H2+ was demonstrated using a strong base and was studied using NMR and UV–vis absorption spectroscopies. The equilibrating excited triplet states of 34+ are reductively quenched by N,N-dimethylaniline assisted by hydrogen bonding to the bridging amide. KW - Dual emission KW - Excited state mixed-valence KW - Electron transfer KW - Ruthenium KW - Terpyridine KW - Amide acidity PY - 2014 U6 - https://doi.org/10.1021/ic5020362 SN - 0020-1669 SN - 1520-510X VL - 53 IS - 24 SP - 12947 EP - 12961 PB - American Chemical Society CY - Washington, DC AN - OPUS4-32536 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hoffmann, Katrin A1 - Behnke, Thomas A1 - Grabolle, Markus A1 - Resch-Genger, Ute T1 - Nanoparticle-encapsulated vis- and NIR-emissive fluorophores with different fluorescence decay kinetics for lifetime multiplexing N2 - Bioanalytical, clinical, and security applications increasingly require simple, efficient, and versatile strategies to measure an ever increasing number of analytes or events in parallel in a broad variety of detection formats as well as in conjunction with chromatographic separation techniques or flow cytometry. An attractive alternative to common optical multiplexing and encoding methods utilizing spectral multiplexing/color encoding and intensity encoding is lifetime multiplexing, which relies on the discrimination between different fluorescent reporters based on their fluorescence decay kinetics. Here, we propose a platform of surface-functionalizable polymeric nanoparticles stained with fluorophores differing in their fluorescence lifetimes as a new multiplexing and encoding approach. Proof-of-concept measurements with different sets of lifetime-encoded polystyrene nanoparticles are presented, obtained via staining of preformed particles with visible (vis)- and near-infrared (NIR)-emissive organic dyes, which display very similar absorption and emission spectra to enable excitation and detection at the same wavelengths, yet sufficiently different fluorescence decay kinetics in suspension, thereby minimizing instrumentation costs. Data analysis was performed with a linear combination approach in the lifetime domain. Our results and first cell experiments with these reporter sets underline the suitability of our multiplexing strategy for the discrimination between and the quantification of different labels. This simple and versatile concept can be extended to all types of fluorophores, thereby expanding the accessible time scale, and can be used, e.g., for the design of labels and targeted probes for fluorescence assays and molecular imaging, cellular imaging studies, and barcoding applications, also in conjunction with spectral and intensity encoding. KW - Fluorescent label KW - Multiplexing KW - Optical KW - encoding KW - Lifetime multiplexing KW - Fluorescence lifetime imaging FLIM KW - Nanoparticles PY - 2014 U6 - https://doi.org/10.1007/s00216-013-7597-3 SN - 1618-2642 SN - 1618-2650 VL - 406 IS - 14 SP - 3315 EP - 3322 PB - Springer CY - Berlin AN - OPUS4-30077 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grabolle, Markus A1 - Pauli, Jutta A1 - Brehm, Robert A1 - Resch-Genger, Ute T1 - Structural control of dye-protein binding, aggregation and hydrophilicity in a series of asymmetric cyanines N2 - Aiming at the rational design and the identification of brilliant fluorescent reporters for targeted optical probes and fluorescence assays in biological matrices, we systematically assessed the correlation between dye–protein binding, dye aggregation, and dye hydrophilicity for bioanalytically relevant fluorescent labels. Here, we report on the influence of sulfonic acid groups on dye aggregation and dye–serum protein interactions exemplarily for a family of NIR-emissive cyanine dyes, the DY-67x fluorophores. For highly hydrophobic dyes like DY-675 and DY-676, which show a strong tendency for aggregation in phosphate buffer saline solution, the dye–protein binding constants determined spectroscopically using a 2-state binding model, which considers only protein-bound and unbound dye molecules, can be influenced by the dimerization of the unbound dyes. To consider and quantify this influence, we expanded this common photometric method to a 3-state model that accounts for the presence of dye aggregates in the binding studies. Our results can be exploited for the screening of fluorescent reporters, efficiently providing information on the size of dye–protein interactions and on maximally achievable fluorescence quantum yields in biological systems. KW - Cyanine dye KW - Dye–protein interaction KW - BSA KW - Binding constant KW - Hydrophilicity KW - Aggregation PY - 2014 U6 - https://doi.org/10.1016/j.dyepig.2013.11.027 SN - 0143-7208 SN - 1873-3743 VL - 103 SP - 118 EP - 126 PB - Elsevier Ltd. CY - Kidlington AN - OPUS4-30054 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Würth, Christian A1 - Grabolle, Markus A1 - Pauli, Jutta A1 - Spieles, Monika A1 - Resch-Genger, Ute T1 - Relative and absolute determination of fluorescence quantum yields of transparent samples N2 - Luminescence techniques are among the most widely used detection methods in the life and material sciences. At the core of these methods is an ever-increasing variety of fluorescent reporters (i.e., simple dyes, fluorescent labels, probes, sensors and switches) from different fluorophore classes ranging from small organic dyes and metal ion complexes, quantum dots and upconversion nanocrystals to differently sized fluorophore-doped or fluorophore-labeled polymeric particles. A key parameter for fluorophore comparison is the fluorescence quantum yield (Φf), which is the direct measure for the efficiency of the conversion of absorbed light into emitted light. In this protocol, we describe procedures for relative and absolute determinations of Φf values of fluorophores in transparent solution using optical methods, and we address typical sources of uncertainty and fluorophore class-specific challenges. For relative determinations of Φf, the sample is analyzed using a conventional fluorescence spectrometer. For absolute determinations of Φf, a calibrated stand-alone integrating sphere setup is used. To reduce standard-related uncertainties for relative measurements, we introduce a series of eight candidate quantum yield standards for the wavelength region of ~350–950 nm, which we have assessed with commercial and custom-designed instrumentation. With these protocols and standards, uncertainties of 5–10% can be achieved within 2 h. PY - 2013 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-294202 SN - 1754-2189 SN - 1750-2799 VL - 8 IS - 8 SP - 1535 EP - 1550 PB - Nature Publishing Group CY - Basingstoke AN - OPUS4-29420 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dietrich, J. A1 - Wünsche von Leupoldt, A. A1 - Grabolle, Markus A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - Thermal and photoinduced electron transfer in directional bis(terpyridine)ruthenium(II)-(bipyridine)-platinum(II) complexes N2 - Metalloligands L1 and L2 consisting of directional bis(terpyridine)ruthenium(II) units and bipyridine moieties were constructed by amide formation. From these metalloligands two Ru–Pt heterobimetallic complexes 1 and 2 were derived by a building-block method by means of platination with [PtCl2(dmso)2]. Both bimetallic complexes 1 and 2 feature metal-to-ligand charge transfer (MLCT) absorptions, and emission occurs at room temperature in fluid solution from ³MLCT(Ru) states in all cases. Energy transfer from platinum to ruthenium is observed in 2 but not in 1 (light harvesting). The one-electron-reduced species [1]– and [2]– were prepared by reduction of 1 and 2 with decamethylcobaltocene. EPR spectra and DFT calculations reveal that the spin density is localized at the tpy–CO/Ru (tpy = terpyridine) site in [1]–, whereas it is centered at bpy–CO/Pt (bpy = 2,2'-bipyridine) in [2]–. Efficient photoinduced electron transfer from triethanolamine to 1 and 2 is feasible by excitation at 500 nm [MLCT(Ru)]. KW - Electron transfer KW - Luminescence KW - Platinum KW - Ruthenium KW - N ligands PY - 2013 U6 - https://doi.org/10.1002/ejic.201201531 SN - 1434-1948 SN - 1099-0682 VL - 2013 IS - 17 SP - 3009 EP - 3019 PB - Wiley-VCH Verl. CY - Weinheim AN - OPUS4-29301 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pauli, Jutta A1 - Licha, K. A1 - Berkemeyer, Janis Manuel A1 - Grabolle, Markus A1 - Spieles, Monika A1 - Wegner, N. A1 - Welker, P. A1 - Resch-Genger, Ute T1 - New fluorescent labels with tunable hydrophilicity for the rational design of bright optical probes for molecular imaging N2 - The rational design of bright optical probes and dye–biomolecule conjugates in the NIR-region requires fluorescent labels that retain their high fluorescence quantum yields when bound to a recognition unit or upon interaction with a target. Because hydrophilicity-controlled dye aggregation in conjunction with homo-FRET presents one of the major fluorescence deactivation pathways in dye–protein conjugates, fluorescent labels are required that enable higher labeling degrees with minimum dye aggregation. Aiming at a better understanding of the factors governing dye–dye interactions, we systematically studied the signal-relevant spectroscopic properties, hydrophilicity, and aggregation behavior of the novel xS-IDCC series of symmetric pentamethines equipped with two, four, and six sulfonic acid groups and selected conjugates of these dyes with IgG and the antibody cetuximab (ctx) directed against the cancer-related epidermal growth factor (EGF) receptor in comparison to the gold standard Cy5.5. With 6S-IDCC, which displays a molar absorption coefficient of 190 000 M–1 cm–1 and a fluorescence quantum yield (Φf) of 0.18 in aqueous media like PBS and nearly no aggregation, we could identify a fluorophore with a similarly good performance as Cy5.5. Bioconjugation of 6S-IDCC and Cy5.5 yielded highly emissive targeted probes with comparable Φf values of 0.29 for a dye-to-protein (D/P) ratio <1 and a reduced number of protein-bound dye aggregates in the case of 6S-IDCC. Binding studies of the ctx conjugates of both dyes performed by fluorescence microscopy and FACS revealed that the binding strength between the targeted probes and the EGF receptor at the cell membrane is independent of D/P ratio. These results underline the importance of an application-specific tuning of dye hydrophilicity for the design of bright fluorescent reporters and efficient optical probes. Moreover, we could demonstrate the potential of fluorescence spectroscopy to predict the size of fluorescence signals resulting for other fluorescence techniques such as FACS. KW - Cyanine KW - Cetuximab KW - IgG KW - Protein labeling KW - Fluorescence quantum yield KW - Hydrophilicity KW - Dimerization constant PY - 2013 U6 - https://doi.org/10.1021/bc4000349 SN - 1043-1802 SN - 1520-4812 VL - 24 IS - 7 SP - 1174 EP - 1185 CY - Washington, DC AN - OPUS4-29076 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Felbeck, Tom A1 - Behnke, Thomas A1 - Hoffmann, Katrin A1 - Grabolle, Markus A1 - Lezhnina, M.M. A1 - Kynast, U.H. A1 - Resch-Genger, Ute T1 - Nile-red-nanoclay hybrids: Red emissive optical probes for use in aqueous dispersion N2 - Water-dispersible and (bio)functionalizable nanoclays have a considerable potential as inexpensive carriers for organic molecules like drugs and fluorophores. Aiming at simple design strategies for red-emissive optical probes for the life sciences from commercial precursors with minimum synthetic effort, we systematically studied the dye loading behavior and stability of differently functionalized laponites. Here, we present a comprehensive study of the absorption and emission properties of the red emissive hydrophobic and neutral dye Nile Red, a well-known polarity probe, which is almost insoluble and nonemissive in water. Adsorption of this probe onto disk-shaped nanoclays was studied in aqueous dispersion as function of dye concentration, in the absence and presence of the cationic surfactant cetyltrimethylammonium bromide (CTAB) assisting dye loading, and as a function of pH. This laponite loading strategy yields strongly fluorescent nanoclay suspensions with a fluorescence quantum yield of 0.34 at low dye loading concentration. The dye concentration-, CTAB-, and pH-dependent absorption, fluorescence emission, and fluorescence excitation spectra of the Nile-Red6#8211;nanoclay suspensions suggest the formation of several Nile Red species including emissive Nile Red monomers facing a polar environment, nonemissive H-type dimers, and protonated Nile Red molecules that are also nonfluorescent. Formation of all nonemissive Nile Red species could be suppressed by modification of the laponite with CTAB. This underlines the great potential of properly modified and functionalized laponite nanodisks as platform for optical probes with drug delivery capacities, for example, for tumor and therapy imaging. Moreover, comparison of the Nile Red dimer absorption spectra with absorption spectra of previously studied Nile Red aggregates in dendrimer systems and micelles and other literature systems reveals a considerable dependence of the dimer absorption band on microenvironment polarity which has not yet been reported so far for H-type dye aggregates. KW - Nile Red KW - Dye KW - Laponite KW - Nanoclay KW - Photoluminescence KW - Fluorescence KW - Polarity probe KW - Aggregate KW - Dimer PY - 2013 UR - http://pubs.acs.org/doi/pdf/10.1021/la402165q U6 - https://doi.org/10.1021/la402165q SN - 0743-7463 SN - 1520-5827 VL - 29 IS - 36 SP - 11489 EP - 11497 PB - American Chemical Society CY - Washington, DC AN - OPUS4-29017 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -