Chapter 5 - Functional dyes for surface plasmon resonance-based sensing system

Abstract

Surface plasmon resonance (SPR) is a unique optical transducer with numerous applications in a variety of molecular interactions. SPR can be used to probe refractive index changes that occur at the interface. Surface plasmon waves (SPWs) are excited at the interface between a thin, highly reflecting metal layer (e.g., silver or gold) and a sample by coupling through a substrate with a high refractive index. SPWs are transverse waves with an oscillating electric field normal to the surface. Because surface plasmons have only an electric field component, which is normal to the surface, p-polarized light is required to satisfy the boundary conditions necessary to excite SPR. At the SPR angle, the energy of the metal surface coincides with the incident photon and the charge density wave. The photon energy is then transferred to the SPW, which results in energy loss from reflected intensity. This phenomenon can be observed as a sharp dip in the reflected light intensity. Outside the metal, an evanescent electric field exists. This evanescent wave is part of the internally reflected light beam and partially penetrates into the lower refractive index medium. The evanescent wave is the “sensing” component and can interact optically with compounds close to or at the surface. Changes in the optical properties of this region will influence the SPR angle and account for the use of SPR for sensing purposes.