In situ surface plasmon resonance analysis of dextran monolayer degradation by dextranase

Surface plasmon resonance (SPR) has been employed to investigate the hydrolytic degradation of thiolated dextran monolayers on silver by the enzyme dextranase. The influence of pH upon the kinetics of this enzyme-catalyzed degradative reaction has been demonstrated, and SPR experiments reveal that dextranase does not completely remove the thiolated dextran monolayers, even at the enzyme's most active pH. X-ray photoelectron spectroscopy and atomic force microscopy results support this observation, as do SPR measurements of protein adsorption to degraded samples, which show significant protein resistance after degradation. It is suggested that incomplete degradation occurs due to an inability of the enzyme to process, or complex with, the derivatized thiol bound portions of individual dextran macromolecules close to the silver surface.