FIELD: biological, biochemical and chemical research such as measurement of insignificant conformational changes in molecules and in reactions of electron transfer. SUBSTANCE: according to invention light from light source 14 is focused by prism on thin metal film 15 on which detected molecules are adsorbed. Total internal reflection of incident laser beam is collected neither by single-element or matrix photodetectors, which are widely utilized in preceding work but by differential position-sensitive or intensity-sensitive photodetector 12. Ratio of differential signal to summary signal from mentioned differential position-sensitive or intensity-sensitive photodetector makes it possible to measure accurately shift angle of surface plasma resonance caused by adsorption of molecules on metal films 15 or by conformational changes in specified adsorbed molecules. EFFECT: invention does not require numerical approximation for determination of resonance angle and proposed device is compact and insensitive to backg
