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A structurally correlated series of cell-permeant thiophene fluorophores, characterized by intense green or red fluorescence inside live mouse embryonic fibroblasts, was developed. The fluorophores displayed rapid internalization, excellent retention inside the cells, and high optical stability in the cytosolic environment and did not alter cell viability and reproducibility. Depending on the molecular structure, they experienced distinct fate inside the cells: from bright and lasting staining of the cytoplasm to selective tagging of a small set of globular proteins.

In our search for thiophene fluorophores that can overcome the limits of currently available organic dyes in live-cell staining, we synthesized biocompatible dithienothiophene-S,S-dioxide derivatives (DTTOs) that were spontaneously taken up by live mouse embryonic fibroblasts and HeLa cells. Upon treatment with DTTOs, the cells secreted nanostructured fluorescent fibrils, while cell viability remained unaltered. Comparison with the behavior of other cell-permeant, newly synthesized thiophene fluorophores showed that the formation of fluorescent fibrils was peculiar to DTTO dyes. Laser scanning confocal microscopy of the fluorescent fibrils showed that most of them were characterized by helical supramolecular organization. Electrophoretic analysis and theoretical calculations suggested that the DTTOs were selectively recognized by the HyPro component of procollagen polypeptide chains and incorporated through the formation of multiple H-bondings.

Abstract: We investigated the uptake and release of labeled antibodies from pH-sensitive hydrogel microparticles (i.e. microgels) by means of fluorescence analysis of labeled biological samples. The poly(methacrylic acid) (PMAA) hydrogel is a carbon-based network having carboxylic groups on the surface that dissociate according to their acid–base equilibrium. The ability of the PMAA microgel to encapsulate and release anti-CD4 and anti-CD8 monoclonal antibodies (MAbs), differing for the isotype and labeled with highly photostable fluorophore, was studied in solution by photoluminescence spectroscopy. The experimental results indicated that the uptake and release of the tested antibodies were controlled by pH. Furthermore, confocal microscopy analysis in the solid state revealed that the distribution of the labeled antibodies either on the surface or in the core of the microgel matrix was related to the specific properties of these MAbs. [Copyright &y& Elsevier]