ELSEVIER Sensors and Actuators B 35-36 (1996) 497-505 B Detection of non-specific protein adsorption at artificial surfaces by the use of acoustic plate mode sensors R. Dahint ~,*, R. Ros SeigeP, P. Harder a, M. Grunze -~, F. Josse b aAngewandte Physikalische Chemie, UniversitiltHeidelberg, lm Neuenheimer Feld 253, 69120 Heidelberg, Germany bDepartment of Electrical and Computer Engineering and Microsensor Research Laboratory, Marquette University, Milwaukee, W153233, USA Abstract The interaction of proteins with artificial surfaces is important to many medical and biochemical applications. Su h examples in- volve 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 characteris- tics at these surfaces would, therefore, support technological progress. Contrary to traditional immunoassays, acoustic wave-based sen- sors 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 bind- ing of native proteins and a subsequent unfolding process. Complete regeneration of the sensor element is achieved by the use of so- dium dodecylsulfate. Keywords: Protein adsorption: Artificial surfaces: Acoustic plate mode sensors 1. Introduction A detailed understanding of the interaction of proteins with artificial surfaces is critical for many medical and biochemical applications [1,2]. Such knowledge could, for example, improve the implementation of synthetic coatings for catheters and prostheses which come in con- tact with biological fluids. Other examples involve the non-specific adsorption of pharmacological proteins at the walls of a container, which may reduce their activity [3], and the adhesion of pathogenic bacteria, which is deter- mined by the affinity of the surface towards proteins [4]. What is ueeded to support technical progress is a rapid, on-line analytical tool capable of detecting proteins and determining the specific adsorption behavior at various surfaces. Moreover, well-defined surface characteristics * Corresponding author. 0925-4005/96/$15.00 © 1996 ElsevierScienceS.A. All rights reserved Pll $0925-4005(96)02072-2 are required in order to create general model systems for studying the effects of surface properties on protein ad- sorption. Several approaches have been investigated and used for real-time, on-line monitoring of biospecific interac- tions. They include optical, electrical, electrochemical and acoustic techniques. Among the various technologies be- ing investigated, acoustic wave-based sensors apparently offer the opportunity to establish a low-cost system for a one-step detection of proteins [5]. In particular, the use of acoustic plate modes (APMs) has proven to be a promis- ing concept as sensor electrodes and analyte are strictly separated, thus facilitating the sensor cleaning and prepa- ration processes. Contrary to the traditional time- consuming multi-stage immunoassay, they allow a direct, rapid and on-line detection of label-free proteins, thus providing the opportunity to study the kinetics of the binding process [6,7]. Moreover, onl/a small amount of analyte is required for the analysis.