Simulation of a High Sensitive Surface Plasmon Resonance Biosensor for Detection of Biomolecules: effect of metal index

Abstract – The Kretschmann configuration is a well-established method for exciting surface plasmons, widely used in optical sensing through Surface Plasmon Resonance (SPR). This study presents a comparative analysis of the sensitivity of Kretschmann-based SPR structures using gold (Au) and silver (Ag) as plasmonic layers. Both simulation and experimental results were used to evaluate the optical response of each metal under varying refractive indices of the surrounding medium.

The findings indicate that silver exhibits a narrower resonance curve and slightly higher sensitivity in terms of angular shift per refractive index unit (RIU), due to its lower optical losses. However, gold offers superior chemical stability, making it more suitable for practical and long-term applications, despite having a broader resonance

The system was modelled using the transfer matrix method (TMM) to simulate the reflectance of a p-polarized light beam incident on a multi-layer structure composed of a BK7 glass prism, a thin metal film (either Au or Ag), and a dielectric sensing medium. The metal layer thickness was optimized to ensure efficient plasmon excitation. Refractive index changes in the sensing medium (from 1.33,1.38) were introduced to assess angular sensitivity. Optical constants for Au and Ag were taken from experimental data (e.g., Johnson and Christy).