Surface plasmon resonance interferometry for biological and chemical sensing

Surface plasmon resonance (SPR) interferometry is reported as a novel techn ique for biological and chemical sensing, which employs not only the amplit ude of a resonantly reflected light wave, but its phase as well. In this co nnection, the phase behavior under SPR has been comprehensively described b y 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 th e resonant reflectivity contour. The 'step' has been imaged by the fringe o f a 2-dimensional interference pattern where one coordinate was the inciden ce 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 syst em passes through the optimum SPR conditions. Monitoring the inversion prov ides for ultra-high sensitivity to an analyte while recording angular posit ion of the 'step', does for dynamic range as wide as that of traditional SP R sensors. The SPR interferometry technique has confirmed theoretical findi ngs and opened up new possibilities for (bio)chemical sensing. (C) 1999 Els evier Science S.A. All rights reserved.