Analyzing the Performance of Plasmonic Resonators for Dielectric Sensing

The frequency shift of the plasmon resonances of metallic nanostructures upon changes in the surrounding bulk refractive index, coating with dielectric layers, and attachment of dielectric spheres is investigated. A general figure of merit (FOM) for the sensing capability of a given resonator is introduced and applied to those three situations. It is based on statistical analysis and an analytical expression for the resonance change. The latter is derived in a perturbation approach and yields a direct connection between the field localization and the resonator response. The scaling of this FOM with the size of the resonator and the analyte are discussed. We show that the optimal resonator strongly depends on the analyte under consideration. These concepts and their limitations are illustrated based on full numerical simulations of surface-supported crescent-shaped gold nanostructures.