Fluorescent molecular nanocrystals anchored in sol-gel thin films: a label-free signalization function for biosensing applications

A DNA sensor based on highly fluorescent and photostable molecular nanocrystals has been investigated. These nanocrystals are confined in a sol-gel thin film by a simple one-step process. After controlled dissolution of the sol-gel thin film layer-by-layer, nanocrystals emerge from the silicate matrix. Hairpin-shaped DNA fragments, functionalized by a probe molecule, were chemically bound to these nanocrystals. This grafting brings molecular probes close to the nanocrystal surface, resulting in quenching of the nanocrystal fluorescence by Fo ̈ rster Resonance Energy Transfer. After hybridization of the hairpin with their complementary DNA, they become unfolded, moving the probes away from the nanocrystals. This ''turns on'' the fluorescence of the nanocrystals and allows the hybridization detection of non-fluorescent DNA to be achieved. These first results on fluorescent nanocomposite coatings open up promising possibilities for making label-free generic sensors.