Preparation of a new core–shell Ag@SiO2 nanocomposite and its application for fluorescence enhancement

Ag@SiO2 nanoparticles with different shell thicknesses were synthesized via modified Stöber method. Rhodamine B isothiocyanate was covalently bound onto the surface of Ag@SiO2 nanoparticles to form fluorescent core–shell Ag@SiO2 nanocomposites. Effects of shell thickness on the fluorescence enhancement were examined using the corresponding nanobubbles prepared by cyanide etching as a control. The result showed that the fluorescence enhanced as the shell thickness increased till the distance between fluorophore and metal core reached about 75 nm with the optimal enhancement factor of ∼5-folds. Further increasing of fluorophore–metal distance caused a decrease in the enhancement factor.