BSA adsorption on a plasma-deposited silver nanocomposite film controls silver release: A QCM and XPS-based modelling

The adsorption of a model protein, the bovine serum albumin (BSA), on plasma-deposited silver nanocomposite thin films was investigated in situ by quartz crystal microbalance (QCM) and ex situ by X-ray photoelectron spectroscopy (XPS). For comparison, BSA adsorption was also studied on pure silver sample and on the polymeric matrix without silver nanoparticles. Both techniques showed that BSA adsorption systematically occurred, regardless of the chemical composition of the solid surface. BSA adsorption was found to be a fast and irreversible process. For the adsorbed BSA layer characterization, a general island model was considered. The height of the protein islands (h) and their surface coverage (γ) were estimated from combined QCM and XPS data. On the polymeric matrix, the surface coverage was low whereas on pure silver sample and on the nanocomposite film, it was significantly increased. From QCM measurements, mass loss at a constant rate, ascribed to the release and dissolution of Ag particles from the nanocomposite film into the surrounding solution, was observed before and after BSA adsorption, with two different associated rates. The decrease of the silver release rate after BSA adsorption is explained by silver particles coverage by protein islands. BSA molecules adsorbed on silver nanoparticles have a “blocking” effect, decreased the rate of silver nanoparticle release. However, silver dissolution as Ag+ ions may still occur.