Metal-dielectric nanostructures with quadrupolar response for sensing applications

Abstract

Metal-dielectric core-shell nanoparticles have attracted a great amount of interest in nano photonics due to the wide variety of applications. The aim of this study was to look at the effect of refractive index of the surrounding medium on Absorption Cross Section (ACS) of core-shell structures with various combinations of interfaces such as Ag–TiO₂, TiO₂–Ag, TiO₂–Ag–TiO₂. SPR peak exhibited red-shift with an increase in the refractive index of the medium. When size of the core metal is increased, besides dipolar peak, other multipolar peaks emerge. By optimising parameters such as core radius and shell thickness, quadrupolar peak can be made stronger. Quadrupolar peak is sharper compared to dipolar peak which yields higher sensitivity. Besides the shift of quadrupolar peak of SPR with respect to refractive index exhibits more linearity. Sensitivity can be optimized by trying different combinations and their parameters. Using simulation, we demonstrated the 3 systems optimized sensitivity for shell thickness of 20 nm, 15 nm, 10 nm and 5 nm. And for core-shell systems, maximum sensitivity optimized for 5 nm shell thickness and for multilayer case 20 nm outer shell thickness is optimized. These optimized metal-dielectric nanostructures are especially suited for biosensing applications.