Silica nanowire assemblies as three-dimensional, optically transparent platforms for constructing highly active SERS substrates

Abstract

Three-dimensional surface-enhanced Raman scattering (SERS) substrates are prepared via the in situ deposition of silver nanoparticles (AgNPs) on silica nanowire (SiO₂ NW) assemblies, either in a free-standing membrane structure or as an optically transparent film supported on Scotch tape. The negatively charged surface of the SiO₂ NW favors Ag⁺ ion enrichment around itself, with the ions forming densely deposited AgNPs on the NW after reducing agents are added to the solution. A SERS substrate with high sensitivity is achieved owing to abundant “hot spots” generated by the inter-AgNP gaps in the 3D geometry of the NW networks. The AgNP-deposited SiO₂ NW membrane has a SERS enhancement factor of 2.9 × 10⁸ and a detection limit of 10⁻⁹ M towards 4-mercaptopyridine probing and 10⁻⁸ M towards dithiocarbamate pesticide (i.e., thiram) probing. Moreover, the AgNP-deposited, Scotch tape-supported SiO₂ NW film achieves non-invasive, direct detection of real-world surfaces due to its high sensitivity, high flexibility and optically transparent properties.