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 - TY - JOUR A1 - Hoffmann, Katrin A1 - Behnke, Thomas A1 - Drescher, Daniela A1 - Kneipp, Janina A1 - Resch-Genger, Ute T1 - Near-infrared-emitting nanoparticles for lifetime-based multiplexed analysis and imaging of living cells N2 - The increase in information content from bioassays and bioimaging requires robust and efficient strategies for the detection of multiple analytes or targets in a single measurement, thereby addressing current health and security concerns. For fluorescence techniques, an attractive alternative to commonly performed spectral or color multiplexing presents lifetime multiplexing and the discrimination between different fluorophores based on their fluorescence decay kinetics. This strategy relies on fluorescent labels with sufficiently different lifetimes that are excitable at the same wavelength and detectable within the same spectral window. Here, we report on lifetime multiplexing and discrimination with a set of nanometer-sized particles loaded with near-infrared emissive organic fluorophores chosen to display very similar absorption and emission spectra, yet different fluorescence decay kinetics in suspension. Furthermore, as a first proof-of-concept, we describe bioimaging studies with 3T3 fibroblasts and J774 macrophages, incubated with mixtures of these reporters employing fluorescence lifetime imaging microscopy. These proof-of-concept measurements underline the potential of fluorescent nanoparticle reporters in fluorescence lifetime multiplexing, barcoding, and imaging for cellular studies, cell-based assays, and molecular imaging. KW - Fluorescence lifetime imaging microscopy KW - FLIM KW - Lifetime multiplexing KW - Near infrared KW - NIR KW - Cell imaging KW - Nanoparticles PY - 2013 U6 - https://doi.org/10.1021/nn4029458 SN - 1936-0851 VL - 7 IS - 8 SP - 6674 EP - 6684 PB - ACS Publ. CY - Washington, DC, USA AN - OPUS4-29031 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -