Tailoring Plasmonic Properties of Silica-Coated Gold and Silver Nanostructures

Abstract

The performance of plasmonic sensors is primarily determined by two critical factors: the bulk refractive index sensitivity (RIS) and the linewidth (or full-width at half maximum, FWHM) of the localized surface plasmon resonance (LSPR) peak. To achieve optimal sensor functionality, it is essential to maximize RIS while maintaining a narrow resonance spectrum. These parameters are often collectively assessed using the product RIS and FoM, where FoM (figure of merit) is defined as RIS/FWHM. While complex plasmonic nanostructures are widely recognized for their high sensitivity, they frequently suffer from broad LSPR peaks, which can compromise detection limits. In this research, we utilized full-wave electromagnetic analysis, grounded in Mie theory, to model dielectric-shell/metal-core nanoshells—specifically Au coated SiO₂ and Ag coated SiO—as effective LSPR sensors. By optimizing the nanoshells' geometry, we calculated the highest RIS × FoM values, obtaining ~479 nm/RIU² for Ag coated SiO and ~364 nm/RIU² for Au coated SiO₂. Our findings indicate that this multilayer core-shell design can be extended to other material systems, enabling the development of plasmonic sensors with improved accuracy, stability, and sensitivity across a wide spectral range.

Keywords- Localized Surface Plasmon Resonance, Bulk Sensitivity (RIS), Figure Of Merit (FoM)