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, 6C, 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
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