Modified Stöber synthesis of SiO2@Ag nanocomposites and their enhanced refractive index sensing applications

Abstract

Core-shell type nanostructures (metal nanoparticles decorated dielectric spheres) are of particular interest based on their application potentials ranging from catalysis, bio-sensing to optical devices because of their inherent characteristic physico-chemical properties. Herein, we utilized silica (SiO2) as the dielectric cores and Ag as the metal shell nanostructures. In this study, we carefully modified the conventional Stöber process for the in-situ one step synthesis as well as functionalization of large and highly uniform silica particles with the universally soluble homogenous polymer PVP (polyvinyl pyrrolidone). This facilitates cohesive control of uniform mass transfer of Ag+ metal ions onto the silica surface, thereby enabling their sequential reduction to zerovalent Ag atoms (in the presence of slightly excess NaOH), as confirmed from the detailed spectroscopic and microscopic measurements. The precise role of PVP in the stabilization as well as sequential reduction of the Ag nanoparticles onto the dielectric silica surface is prudently demonstrated through FTIR data analysis. The nonlinear dependence of the plasmonic peak wavelength on the refractive index (RI) describes the intriguing light-matter interaction of core-shell type nanostructures, disentangling the surface plasmon contribution at the dielectric-metal interfaces in a rigorous manner, quantifying the plasmonic ultra-sensitivity and figure of merit of our as-prepared optical metamaterials.