Exploring surface plasmon-polariton resonance (SPR) in an interferometer configuration

Abstract

An optical, two-channel molecular sensor design using surface-plasmon polariton resonance (SPR) in a Mach-Zehnder interferometer was devised for studying the enhancement due to the presence of interferometry. The objective was to detect very small quantities of gas molecules with molecular weights in the range of 17 to 28 Daltons using either the signal from the transmitted laser beam or the interference image that can be computer analyzed. Dry air in humid air and pure ammonia gas diluted in dry air were studied. Initial studies gave detection sensitivities of better than 70 parts per 108 for changes in refractive index of the gas. With interferometry, recorded signals were 40X greater than with the normal SPR technique.