Lateral mobility of proteins adsorbed on or embedded in polyelectrolyte multilayers

We present the first results relative to the diffusion process of proteins (human serum albumin) adsorbed on or embedded in poly(sodium 4-styrenesulfo nate)/poly(allylamine hydrochloride) polyelectrolyte multilayer films by us ing fluorescence recovery after photobleaching. At least two populations of adsorbed proteins exist on the top or within the multilayer architectures. One population, which typically represents 50-70% of the adsorbed proteins , corresponds to proteins that are able to diffuse laterally along the surf ace or in the multilayers, whereas the others diffuse more slowly or seem a lmost immobile over the experimental time scale. This constitutes a key res ult for the practical applications of the polyelectrolyte multilayers as ta rgeted biomaterial coatings. Surprisingly, the diffusion coefficients of th e mobile proteins that are embedded in the multilayers are comparable with the diffusion coefficients of the mobile proteins adsorbed on top of the mu ltilayers. The diffusion coefficients, which are 1 order of magnitude small er than on rigid substrates such as silica or poly(methyl methacrylate), ar e of the order of 10(-10) and 10(-11) cm(2)/s.