The Distance-Dependent Fluorescence Enhancement Phenomena in Uniform Size Ag@SiO2@SiO2(dye) Nanocomposites

Ag@SiO2@SiO2(FITC) nanocomposites were prepared by the simple polyol process and Stober method. Fluorescence enhancement of fluorescein moiety (fluorescein isothiocyanate, FITC) was investigated in the presence of silver nanoparticles in Ag@SiO2-X@SiO2(FITC) system with varying thickness (X nm) of first silica shell. Maximum enhancement factor of 4.3 fold was achieved in Ag@SiO2-8@SiO2(FITC) structure with the first silica shell thickness of 8 nm and the average separation distance of 11 nm between the surface of silver nanoparticle and fluorescein moiety. The enhancement is believed to be originated from increased excitation rate of fluorescein moiety due to concentrated local electromagnetic field which was improved by interaction of light with silver nanoparticles.