Surface-Enhanced Fluorescence on SiO2-Coated Silver Island Films

Abstract

Fluorescence is one of the molecular spectroscopic properties that is enhanced by placing the molecule on the rough surface of a coinage metal. The surface-enhanced fluorescence (SEF) can be directly observed in steady-state fluorescence experiments. The observations are the results of a delicate balance between the enhanced emission and the quenching due to energy transfer to nonradiative surface plasmons. In the present report, SiO2-coated silver films were fabricated at varying dielectric thickness. The surface of the films was analyzed with the use of atomic force microscopy (AFM) and X-ray photoelectron spectroscopy (XPS). AFM confirms the surface roughness and XPS analysis indicates that the SiO2 coverage was successful. SEF and SERS (surface-enhanced Raman scattering) were observed on active 6, 10, and 14 nm silver films coated with SiO2. Similar results were obtained with a 6 nm silver film coated with 6 nm SiO. The SEF work was carried out on fluorescent molecules with different quantum yield, and the typical enhancement factor obtained for the fluorescent signal was approximately 10. Both the SiO2 and SiO overlayers provide stable surfaces with well-defined hydrophilic properties. Such stable constructions have applicability towards the advancement of SERS and SEF as routine analytical techniques in bio- and chemical sensors.