Fluorescent nanotools for biotechnology: disclosure of the molecular features ruling the brightness of dye-silica nanoparticles

Fluorescent detection tools are widely exploited in modern biochemical research and clinical diagnosis; among various materials, hybrid dye-silica nanoparticles are attracting raising interest. The photophysical properties of such materials are strongly dependent on the dispersion of dye molecules throughout the silica matrix, ruled by molecular events occurring during particle formation. In this respect we investigated the role of dyes (indocarbocyanines) hydrophilicity in determining the final dispersion of fluorophores in the silica phase of hybrid nanoparticles (d: 50±2 nm) produced by the microemulsion technique, where particle formation results from the diffusion of the silica precursor (TEOS) and dye molecules in the aqueous core of reverse micelles. It was established that fluorophores dispersion increases as hydrophilicity decreases, likely due to a correspondent decrease of the dye/TEOS diffusion rate ratio toward the water pool. Consequently, by progressively decreasing the hydrophilicity of the dyes it was possible to enhance the nanoparticles overall brightness from 4 to 500 times with respect to the fluorophore in solution.