Cell penetrating silica nanoparticles doped with two-photon absorbing fluorophores

Organosilica nanoparticles, doped with two-photon absorbing distyrylbenzene derivatives, were prepared and studied as cell staining agents. Two dyes were used, bearing either two peripheral dimethylamino groups or one dimethylamino and one cyano group. Due to the internal charge transfer character of their excited state, the dyes employed show a red-shifted quenched emission in polar solvents. Once included in the particles, the properties of the two dyes undergo a substantial variation. Particles doped with the cyano substituted distyrylbenzene show a remarkable emission quantum yield in water, probably due to solvent exclusion from the nanoparticle core. To the contrary, the emission of the particles containing the di-dimethylamino substituted dye is substantially quenched. Fluorescence emission induced by two-photon absorption follows the same behaviour. The doped nanoparticles can be rapidly internalized by tumour cells with accumulation limited to the cytoplasm and show no cytotoxicity at low concentrations