Surface Plasmon Resonance Biosensors

Abstract

Surface plasmon resonance (SPR) is a real-time, label-free, optical detection method for studying the interaction of soluble analyte with immobilized ligand. SPR occurs when light is internally reflected at the interface between a medium of high refractive index, a thin layer with good electric conductivity, and a medium of low refractive index.1 The evanescent wave that develops at the interface interacts with free electrons in the conductive layer and gives rise to so-called plasmons. The energy for this interaction is lost from the reflected light, resulting in a minimum of the reflected intensity at the resonance angle. The evanescent wave extends only a few hundred nanometers into the medium of lower refractive index and decays exponentially over a fraction of the wavelength. The propagation of the evanescent wave along the interface and thus the resonance angle depend on the refractive index in this thin layer adjacent to the interface.