A Theoretical Model for Determination of Optimum Metal Thickness in Kretschmann Configuration Based Surface Plasmon Resonance Biosensors

Surface plasmon resonance (SPR) is one of the most exciting surface-sensitive methods for bio-molecular interaction analysis (BIA) currently available to researchers. It features surface-sensitive response, label-free detection, and real-time measurement capability. The most important characterizing parameter for an SPR biosensor is its sensitivity. A sensor with higher sensitivity is desired for detecting even minute changes in the sensing layer refractive index. However, sensitivity of SPR sensors based on Kretschmann configuration depends on some crucial parameters, thickness of the metal film being one of them. Thus, determination and choice of optimum metal thickness for the specific sensing conditions is pivotal for enhanced performance and reduction of false alarm occurrence. Hence, in this paper a comprehensive analytical model is developed for the optimization of metal thickness of an SPR bio-sensor. This theory provides the direct relationship between the performance characteristic of the sensor, minimum reflectance (R-min) to the design parameter metal thickness. The proposed analytical model is verified using finite-difference time-domain simulations which match with the theoretical results with negligible error.