Application of optical reflectometry for characterization of polyelectrolyte–protein multilayers

It is known that the build-up of polyelectrolyte multilayers can be followed in situ by means of stagnation point optical reflectometry. Application of optical reflectometry to characterization of multilayers obtained by exposing a suitable substrate to solutions of a cationic homopolymer and an oppositely charged protein was investigated. In all experiments, bovine serum albumin (BSA) was used as the negatively charged component. The weak polyelectrolyte poly(dimethylaminoethyl)methacrylate (PAMA) or the strong polyelectrolyte poly(2-vinyl-n-methylpyridinium iodide) (PVP+) was used as the cationic homopolymer. Silica in the form of silicon wafers carrying an oxide layer was used as the solid substrate and potassium chloride or phosphate buffer were used as the supporting electrolyte. The influence of ionic strength, pH, type of cationic homopolymer (strong or weak), and protein concentration were investigated. It was shown that stagnation point optical reflectometry can be a useful method for characterization of the formation of multilayers containing polyelectrolyte and protein layers.