Role of salts on BSA adsorption on stainless steel in aqueous solutions.: I.: FT-IRRAS and XPS characterization

The understanding of protein interaction with metal surfaces has become a key question for the use of materials in medicine, in the food industry or in marine environment in connection with the process of biofouling. However, the role of the various salts present in natural seawater has never been systematically investigated. In the present work, we studied the adsorption of a protein, bovine serum albumin (BSA), on stainless-steel surfaces in artificial seawater and in aqueous solutions containing NaCl, NaCl + CaCl2 and NaCl + MgCl2, the total concentration of salts being identical to that of the natural seawater (36 g l(-1)); the BSA concentration was fixed at 20 mg l(-1). After rinsing and drying, the surface was analysed by Fourier transform infrared reflection-adsorption spectroscopy (FT-IRRAS) and x-ray photoelectron spectroscopy (XPS). After immersion in aqueous solutions containing NaCl or NaCl + CaCl2 and rinsing in saline solutions, the amount of adsorbed BSA is small. It increases by almost one order of magnitude if the immersion is performed in NaCl + MgCl2 aqueous solution; after 24 h of immersion it reaches a saturation value very close to that attained in natural seawater. At saturation of the stainless-steel surface by the protein, the XPS metal signals were still detected, suggesting that the protein layer is heterogeneous, leaving patches of the surface almost uncovered. The amount of adsorbed BSA is reduced by almost one order of magnitude when the samples are rinsed in pure, demineralized water due to the dissolution of Mg2+ cations and the elimination of loosely adsorbed proteins. The presence of Mg2+ cations within the BSA layer is confirmed by angle-resolved XPS analyses. Copyright (C) 2002 John Wiley Sons, Ltd.