Detection of non-specific protein adsorption at artificial surfaces by the use of acoustic plate mode sensors

The interaction of proteins with artificial surfaces is important to many medical and biochemical applications. Su h examples involve the incorporation of catheters and prostheses as well as the non-specific adsorption of pharmacological proteins at the walls of a container, which may drastically reduce their activity. A fast analytical tool capable of determining the specific adsorption characteristics at these surfaces would, therefore, support technological progress. Contrary to traditional immunoassays, acoustic wave-based sensors allow an on-line and direct detection of label-free proteins, thus saving time and providing 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 (3 (lgO) and fibrinogen with differently terminated self-assembled monolayers (SAMs) of thiols. By this method, both the low affinity of hexa(ethylene glycol)-terminated (HS-(CH2) II-(O-CH2-CH2)6-OH) alkanethiol SAMs and the high affinity of methyl-terminated (HS-(CH2)IrCH3) surfaces towards protein adsorption were confirmed. It was found that the amount of bound proteins depends on the pH of the solution. At low pH values, protein binding to methyl-terminated surfaces is drastically reduced. The adsorption characteristics of fibrinogen at methyl-terminated surfaces are explained by a kinetic model which involves the initial binding of native proteins and a subsequent unfolding process. Complete regeneration of the sensor element is achieved by the use of sodium dodecylsulfate.