Theoretical Studies and Simulation of Gold–Silica–Gold Multilayer “Fanoshells” for Sensing Applications

We develop a theoretical framework, based on a multipole, quasi-static approach, for the prediction of the localized surface plasmon resonances in Fanoshells formed via geometrical symmetry breaking in multilayer nanoshells consisting of a metallic core, a dielectric inner shell, and a metallic outer shell. By tuning the core and shell offsets of a gold–silica–gold multilayer nanoshell, we show that the theoretical model is in good agreement with electrodynamic simulations. The dipolar resonances are more suppressed when the core and the outer shell are both offset and less suppressed when either the core, the inner shell, or the outer shell is offset. Our theoretical model allows us to relate these effects to the coupling constants arising from single symmetry breaking. Using three performance parameters, we propose the outer shell offset as the optimal Fanoshell for sensing applications. This study systematically investigates offset-based, single symmetry-broken, metal–dielectric–metal multilayer nanoshells within the Rayleigh regime.