Synthesis and characterization of fluorescently doped mesoporous nanoparticles for two-photon excitation

The template-directed synthesis of mesoporous silica nanoparticles doped with water-soluble fluorescent dyes optimized for two-photon excitation is described. Two structurally related symmetrical two-photon dyes that possess pyridinium acceptor endgroups conjugated to a fluorenyl core are synthesized by Heck coupling. These dyes display bright fluorescence (Phi approximate to 0.35) under both one- (epsilon approximate to 6 x 10(4) m(-1) cm(-1)) and two-photon excitation (sigma(2) approximate to 1000 GM) and were successfully encapsulated in silica nanoparticles via immobilization through noncovalent interactions. The nanoparticles present a mean diameter of 100 nm and a hexagonal network of mesopores as shown by TEM. Interestingly, the photophysical characteristics of the dyes are retained upon their immobilization into the silica matrix, leading to fluorescent silica nanoparticles with giant/unprecedented TPA cross-section (1 x 10(7) GM). Such nanospheres represent attractive nanoplatforms for the development of biotargeted biocompatible luminescent tracers.