Theoretical understanding of an absorption-based surface plasmon resonance sensor based on Kretchmann's theory.

An optical-absorption-based surface plasmon resonance (SPR) sensor is proposed, and its theoretical aspects are discussed in terms of mathematical descriptions and numerical simulations of the SPR curve. The response theory of the absorption-based SPR sensing is based on the expansion of Kretchmann's SPR theory into the case in which optical absorption in the sensing layer is expressed by the Lorentz model. The numerical simulations were performed using a three-layer Fresnel equation of p-polarization. It was found that SPR curve behavior of the absorption-based SPR sensor depends on the frequency relation between the light source and the optical absorption and the thickness of the metal layer. The SPR curve behavior is divided into three types according to the large, small, and equal relations between excitation and absorption frequencies. Each type of behavior is further divided into two types that are due to thin and thick metal layers. The theory of this new type of sensor based on optical absorption was explained and demonstrated by the simulation of the SPR curves using optical parameters relating to a silver-metal-based SPR sensor.