Fluorescent nanocrystals grown in sol-gel thin films for generic stable and sensitive sensors

Through the sol-gel route, we have well-controlled the preparation of fluorescent organic nanocrystals grown in silicate thin films. This process is based on the confined nucleation and growth of dyes in the pores of wet gels. The resulting nanocomposite sol-gel thin films, coated onto low-cost substrates, exhibit coupled properties: transparency, stability, easy shaping of sol-gel thin films and high fluorescence intensity coming from organic nanocrystals. The sensitivity of the fluorescence intensity of nanocrystals to their environments can be exploited for the development of optical sensors. Indeed, Förster Resonance Energy Transfer can inhibit nanocrystal fluorescence when probe molecules are adsorbed or grafted on the nanocrystal surface after their diffusion through the pores of the sol-gel matrix. We investigated by time-resolved fluorescence spectroscopy the effect of nanocrystal size and probe concentration on the fluorescence quenching in presence of Methylene Blue used in this study as molecular probe. As strong fluorescence quenchings can be achieved, even for low probe concentrations, these hybrid organic-inorganic nanocoposites are promising for the development of sensor devices by increasing their fluorescence contrasts under specific chemical or biological environments.