High resolution surface plasmon resonance spectroscopy

A method for detecting surface plasmon resonance with high resolution (simi lar to 10(-5) degrees or similar to 10(-8) refractive index units) and fast response time (1 mu s) is described. In the method, light is focused throu gh a prism onto a metal film on which molecules to be detected are adsorbed . The total internal reflection of the incident light is collected with a b icell photodetector instead of a single cell or an array of photodetectors that are widely used in previous works. The ratio of the differential signa l to the sum signal of the bicell photodetector provides an accurate measur ement of shift in surface plasmon resonance angle caused by the adsorption of molecules onto the metal films or by conformational changes in the adsor bed molecules. Using the method, we have studied subtle conformational chan ges in redox protein, cytochrome c, due to an electron transfer reaction. ( C) 1999 American Institute of Physics. [S0034-6748(99)02212-1].