Application of protein-coated scanning force microscopy probes in measurements of surface affinity to protein adsorption

Scanning force microscopy (SFM, also called atomic force microscopy, or AFM) has been applied to rapid in situ quantification of surface affinity to protein. The surface affinity was measured by adhesion force measurement with protein-coated SFM probes. Experiments on three model sur faces, -CH3, -COOH and -NH2 terminated self-assembled monolayer (SAM) surfaces, have been performed at pH 4.5 and pH 6.8 environments, using probes covalently coated with bovine serum albumin (BSA). Results show that the hydrophobic -CH3 surface possesses the highest affinity and is independent of pH values. The -COOH and -NH2 surfaces possess pH-dependent affinities. A higher affinity was observed on charged surfaces to proteins with dissimilar net surface charges than with similar net surface charges. Results are corroborated to previous elutability studies on similar systems.