Surface plasmon resonance interferometry for biological and chemical sensing

Abstract

Surface plasmon resonance (SPR) interferometry is reported as a novel technique for biological and chemical sensing, which employs not only the amplitude of a resonantly reflected light wave, but its phase as well. In this connection, the phase behavior under SPR has been comprehensively described by theoretical analysis, numerical simulations, and a number of experiments. Near optimum SPR conditions, a resonant phase dependence is step-like, the ‘step’ being at the reflectivity minimum. For SPR-based sensors, the slope of the ‘step’ can always be made by several orders steeper than that of the resonant reflectivity contour. The ‘step’ has been imaged by the fringe of a 2-dimensional interference pattern where one coordinate was the incidence angle, and the other was the phase. The inversion of the ‘step’ has been observed for the first time during antigen–antibody binding, when the system passes through the optimum SPR conditions. Monitoring the inversion provides for ultra-high sensitivity to an analyte while recording angular position of the ‘step’, does for dynamic range as wide as that of traditional SPR sensors. The SPR interferometry technique has confirmed theoretical findings and opened up new possibilities for (bio)chemical sensing.