Performance mapping of non-concentric SiO2@Ag core-shell nanoparticles for refractive index sensing

This work presents a numerical study of non-concentric SiO 2 @Ag core-shell nanoparticles as refractive-index sensors, using the MNPBEM toolbox. We systematically vary the outer nanoparticle diameter, Ag-shell thickness, and normalized silica-core eccentricity to build performance maps of extinction, resonance wavelength, sensitivity, linewidth, and figure of merit (FOM). The nanoparticle is modeled as a single isolated particle suspended in a homogeneous nondispersive surrounding medium. The refractive index of the medium was varied uniformly from 1.0 to 2.0. The controlled core offset excites mixed bright-dark plasmon modes, yielding narrow Fano-like resonances that improve sensing performance. Large-core (thin-shell) nanoparticles with large position offsets show strong hybridization and strongly increase the local field, characterized by high sensitivities of 250–420 nm/RIU, with very narrow linewidths, providing high sensing performance (FOM > 80 RIU −1 ). The maximum FOM is reached within a design window, rather than at the largest eccentricity or the thinnest shell. This observation underlines the importance of balancing field exposure, radiative damping, mode hybridization, and extinction amplitude simultaneously. We provide quantitative, particle-level design guidance for suspended- or colloidal-based localized surface plasmon resonance sensing platforms.