Surface Plasmon Resonance of A Bimetallic Nanostructured Film for Enhanced Optical Sensitivity

A bimetallic (Ag/Au) nanoslit film is reported on surface plasmon (SP) generation and refractive index (RI) sensitivity. These were compared to gold devices in transmission surface plasmon resonance (tSPR). The bimetallic films have a primary resonant peak that shifts with periodicity and correlates well with Finite-Difference Time-Domain (FDTD) simulation studies. The SPR of bimetallic nanoslit structures is analyzed via a semi-analytical model. The model enables decomposition and quantitative analysis of SP generation at the aperture under plane-wave illumination. The nanostructured, metallic, thin films provide flexibility to integrate with microfluidics, allowing for simplified instrumentation and alignment. Calculation and experimentation demonstrate that bimetallic films afford an increase in RI sensitivity due to the addition of silver along with the biocompatibility of gold. The Ag/Au films were found to be non-diffusing, long-term stable (over several months), and provided an increase in sensitivity (about 53/RIU) over gold equivalents.