Investigation of surface plasmon resonance biosensor sensitivity using Kretschmann ATR theory

Surface plasmon resonance (SPR) is a phenomenon that is frequently employed in biosensing devices. SPR occurs when an incident photon couples to charge density oscillations on a metal surface, exciting a surface plasmon polariton (SPP). SPPs are interface-confined modes that propagate along metal-dielectric structures called waveguides. Attenuated total reflection (ATR) is a method in which a coupling prism is used to excite SPPs in a waveguide. Utilizing the excitation of SPPs by ATR, a SPR biosensor monitors binding interactions at the metal surface of a waveguide in real time, as binding results in a measurable shift in SPP excitation conditions. SPR biosensor performance is limited by low sensitivity of binding detection. Recent evidence suggests that sensitivity can be increased by using SPPs with high propagation lengths. In order to understand the relationship between SPP propagation and biosensor sensitivity, the theory behind SPP excitation in biosensors must be explored. SPR biosensors require the Kretschmann configuration of ATR in which the waveguide’s metal film is exposed for monitoring. While Kretschmann configuration is often used experimentally, comprehensive theoretical models for excitations in this configuration are lacking. Here we discuss development of the electromagnetic theory behind SPR biosensor excitations based off of experimental measurements. Our results show a positive correlation between SPP propagation lengths and biosensor sensitivity, indicating the potential for high sensitivity biosensors that use waveguides tuned to support high propagation SPPs