Contents 1. Introduction
Over the past decades, the surface plasmon resonance (SPR) technology has developed rapidly, and it was widely used in the fields of chemical and biological sensing [1]–[3]. The advantages of the SPR biosensor are real-time, label-free detection, and high sensitivity. The SPR sensing principle is an optical phenomenon in which a TM-polarized light beam satisfies the resonance condition (phase and energy match) and excites the free electron density longitudinal oscillation at the metal/dielectric interface [4] This electronic oscillation is associated with a surface electromagnetic wave, so-called SPW, of which the electric field is maximum at the interface and decreases evanescently into both media. The resonance condition depends on the incident angle, wavelength of the incident light and the dielectric constant of both the metal as well as the sensing dielectric. The SPR sensor has many modulated ways, such as intensity, angle, phase, and wavelength. There are several structures have been used in SPR sensors, including the attenuated total reflection (ATR) in prism couplers, optical waveguides-based, optical fiber-based and diffraction gratings.
