Local Refractive Index Sensitivity of Localized Surface Plasmon Resonance Biosensors

The sensitivity of localized surface plasmon resonance (LSPR) biosensors to a change in the local refractive index (RI) is investigated theoretically. By combining an effective medium theory and a quasistatic theory, analytical expressions for the local RI sensitivity are derived. Electromagnetic simulations show that the expressions can predict the sensitivity well for LSPR biosensors of various sizes and geometries including nanocylinders, nanodisks, nanorods and nanotriangles for both two- and three-layer systems. Like the bulk RI sensitivity, the local RI sensitivity is shown to depend linearly on the resonant wavelength of the biosensors. Other than two parameters used to linearize the dielectric function of the metal core, there are no fitting parameters. Hence, the expressions can be used to predict the local RI sensitivity of LSPR biosensors directly from the resonant wavelength.