Visualisation of the angular dependence of the reflected-radiation phase under conditions of a surface-plasmon resonance and its sensor applications

Angular dependences of the reflected-radiation phase were made visible for the first time under conditions of a surface-plasmon resonance. The dependences were visualised by fringes of an interference pattern in a plane where one coordinate represented the phase and the other corresponded to the angle of incidence. These fringes had an inflection or a kink in the form of a step near a resonance minimum of the reflected-radiation intensity. An inversion of such a step was detected in the course of biological binding on the surface when passing through the optimal conditions for the resonance. This effect made it possible to detect, with a very high sensitivity, changes in the surface state or the presence of a (bio)chemical reagent in the ambient medium. Determination of the angular position of such a step ensured that the dynamic range was wide. The results obtained confirmed conclusively the authors' own model proposed earlier to account for the behaviour of the phase. The method suggested is promising for use in (bio)chemical sensors and analysers.