DETECTION OF NONSPECIFIC PROTEIN ADSORPTION AT ARTIFICIAL SURFACES BYTHE USE OF ACOUSTIC PLATE MODE SENSORS

The interaction of proteins with artificial surfaces is important to m any medical and biochemical applications. Such examples involve the in corporation of catheters and prostheses as well as the non-specific ad sorption of pharmacological proteins at the walls of a container, whic h may drastically reduce their activity. A fast analytical tool capabl e of determining the specific adsorption characteristics at these surf aces would, therefore, support technological progress. Contrary to tra ditional immunoassays, acoustic wave-based sensors allow an on-line an d direct detection of label-free proteins, thus saving time and provid ing the opportunity to monitor the kinetics of the binding process. In this study, Cr/Au-coated acoustic plate mode (APM) sensors have been used to investigate the interaction of immunoglobulin G (IgG) and fibr inogen with differently terminated self-assembled monolayers (SAMs) of thiols. By this method, both the low affinity of hexa(ethylene glycol )-terminated (HS-(CH2)(11)-(O-CH2-CH2)(6)-OH) alkanethiol SAMs and the high affinity of methyl-terminated (HS-(CH2)(11)-CH3) surfaces toward s protein adsorption were confirmed. It was found that the amount of b ound proteins depends on the pH of the solution. At low pH values, pro tein binding to methyl-terminated surfaces is drastically reduced. The adsorption characteristics of fibrinogen at methyl-terminated surface s are explained by a kinetic model which involves the initial binding of native proteins and a subsequent unfolding process. Complete regene ration of the sensor element is achieved by the use of sodium dodecyls ulfate.