Investigation of dual component protein films on graphite with scanning force microscopy

Scanning force microscopy (SFM) was used to examine plasma protein films adsorbed on highly oriented pyrolytic graphite (HOPG). Single component films of bovine serum albumin (BSA) and bovine fibrinogen (BFG) were initially investigated to study the effect of protein solution concentration on film morphology. We then studied the adsorption of BFG to a pre-adsorbed partial layer of BSA. We observed no displacement of the BSA during the time-scale of our experiment. BFG adsorbs on top of the initial BSA layer and on the graphite exposed through voids in the partial BSA film. Different adsorption sites result in distinct conformations of the adsorbed BFG that can be detected with compositionally sensitive contrast mechanisms in SFM. Chemically modified probe tips were employed to elucidate whether mechanical properties or interfacial chemistry of the protein films govern the contrast observed. (C) 2003 Elsevier B.V. All rights reserved.