Abstract

Surface plasmon sensors are used in chemical, gas, and bio-sensing applications. Detection is based on changes in the permittivity of thin interfacial layers¹-². Most surface plasmon detection configurations require expensive optical equipment and a stable optical bench. Thus, surface plasmon sensors have for the most part remained in laboratory environments. The sensors employ a beam of transverse magnetic (TM) polarized light incident through a substrate onto a thin metal film, e.g. Ag or Au. The metal film is chemically sensitized, and exposed to an analyte (see Figure 1.) Above the critical angle, 6_C, the light is totally reflected from the substrate-metal interface, except at a distinct angle of incidence where a surface plasmon mode is generated. At the surface plasmon angle, Ggp, the reflectance reaches a minimum. Ggp is very sensitive to dielectric changes in close proximity to the metal-analyte interface. If the film is sensitized to selectively bind a prescribed chemical, X, a change in permittivity will occur resulting in a shift in 0gp, which can be used to obtain a quantitative measure of the chemical activity of X in the analyte. The basic configuration is shown in Figure 1. All surface plasmon sensors require four basic elements: a source of TM polarized light; a method of coupling this light to a thin metal film through glass so as to achieve incidence angles above the critical angle of reflection; a means of providing a range of incidence angles; and a detector to measure the reflectance as a function of the angle of incidence.

© 1993 Optical Society of America