Organic–inorganic hybrid nanoparticles with enhanced fluorescence

• TPEFA molecules show great fluorescence enhancement when the nanoparticles formed.
• The hybrid nanoparticles can be separated easily by a silica shell coating.
• The nanoparticles have low cytotoxicity and are suitable for cellular imaging.

We report a simple strategy to prepare organic–inorganic hybrid nanoparticles with enhanced fluorescence. A significant fluorescence enhancement was realized by designing a fluorescent small molecule of 9,9′-(6,6′-(2-(4-(1,2,2-triphenylvinyl)phenyl)-9H-fluorene-9,9-diyl)bis(hexane-6,1-diyl))bis(9H-purin-6-amine) (TPEFA) possessing an aggregation-induced emission enhancement effect. Nanoparticles of TPEFA can be formed through molecular self-aggregation by gradually changing the water fraction in the TPEFA mixed solution of tetrahydrofuran (THF) and water, and fluorescence enhancement of about 445-fold was observed after nanoparticle formation. By coating the formed TPEFA nanoparticles with a silica (SiO2) shell, the dispersibility of these fluorescent nanoparticles was greatly improved, becoming easily separated and concentrated after possessing the inorganic silica layer coating. This method solves the difficulty, common among organic nanoparticles, of problematic separation because of the low nanoparticle weight. Cyanic fluorescence from TPEFA@SiO2 nanoparticles can be clearly observed from confocal laser scanning microscope images, and the cyanic spots are bright and well dispersed, which proved the good dispersibility of the prepared fluorescent nanoparticles. Finally, a cellular internalization assay and a cell viability assay demonstrate that the TPEFA@SiO2 nanoparticles can be applied in cellular imaging.

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