Role of salts on the BSA adsorption on stainless steel in aqueous solutions. II. ToF‐SIMS spectral and chemical mapping study

It is now well established that protein adsorption constitutes the first step of the mechanism leading to biofilm formation, which is a precursor of the biofouling. Biofouling is a major problem for any activity in seawater. In order to improve our basic knowledge of the biofilm formation mechanism, the role of salts, dissolved in natural seawater, on protein adsorption on a stainless steel surface have been investigated. Different aqueous solutions were used. They contained different salt mixtures and concentrations (NaCl alone, NaCl + MgCl2, NaCl + CaCl2 and artificial seawater), while keeping the total salt concentration the same as in natural seawater (36 g l(-1)). A protein, bovine serum albumin (BSA), was also added to the saline solutions at 20 mg l-1 concentration. Stainless-steel samples were immersed into the different aqueous solutions for 24 h. After rinsing in demineralized water and drying, the surface of these samples was analysed by time-of-flight secondary ion mass spectrometry (ToF-SIMS). The ToF-SIMS spectra showed an influence of the salts contained in the solutions on the protein adsorption. The role of CaCl2 seemed to be unfavourable whereas MgCl2 was rather favourable for BSA adsorption. The ToF-SIMS molecular mappings showed that all the salts dissolved in water produced micrometre particles at the sample surfaces. These particles mainly constituted Na+, Mg+ or Ca+. Because there was no space correlation with any counter-ions (Cl-, SO4-, OH-, etc.), these particles were not salt residues. Moreover, these particles were found to be the preferential adsorption sites for the proteins. Indeed, the images show that BSA surrounds these metallic spots to form annular-shaped patterns (diameter phi similar to 20 mum. Copyright (C) 2002 John Wiley Sons, Ltd.

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