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.

Plasmon enhanced fluorescence studies from aligned gold nanorod arrays modified with SiO2 spacer layers

“…Studies of SiO2 dielectric coating of plasmon active (fractal) thin gold or silver metal layers have been reported [26][27][28][29]. These studies demonstrated that using thin coating (e.g.…”

“…The schematic shows that the array possesses a 70 nm inter rod distance, a rod diameter 35 nm and rod height of 200 nm. The preparation of the Au nanorod arrays are described elsewhere [27]. In brief, the sample was made on a glass substrate base.…”

Advances in Surface-Enhanced Fluorescence

“…The interaction of fluorophores with metallic particles has been the subject of several publications [27][28][29]. There is reasonable agreement that the maximal enhancements occur about 100 Å from the surface, but some publications report the optimal distance to be as large as 600 Å [30].…”

Polyelectrolyte Layer-by-Layer Assembly To Control the Distance between Fluorophores and Plasmonic Nanostructures

“…Because of these applications, it is important to understand these interactions in terms of the effects of chemical nature, size, shape of the nanostructure, and its distance from the interrogating fluorophore. [15][16][17][18][19] A detail understanding of the MEF and its distance dependence nature is vital for its potential application in biomedical sensing. [20][21][22] Layer-by-layer (LbL) assembly [23][24][25][26][27][28][29][30][31][32][33][34][35][36] is based on the sequential adsorption of polycations and polyanions from dilute aqueous solution onto a solid substrate as a consequence of the electrostatic interaction and complex formation between oppositely charged polyelectrolytes.…”