Reversible and specific interaction of dehydrogenases with a coenzyme-coated surface continuously monitored with a reflectometer.

Reversible affinity binding of NAD-dependent dehydrogenase to an NAD-coated silicon surface ("NAD biochip") has been accomplished. The silicon surface, which is favorable for use with optical techniques because of its excellent reflection properties, was precoated with a polymer to prevent nonspecific and irreversible adsorption. Using a new reflectometry technique based on measurement of the polarization change of light reflected upon the biochip, continuous monitoring of the affinity binding and subsequent desorption of alcohol dehydrogenase and lactate dehydrogenase from the NAD surface were possible; allowing repeated use of the same NAD chip--an advantage when the assay was carried out in a continuous reflectometer. With a flow rate of 0.5 ml/min, response times on the order of 30 s were obtained.