Formation and stability of poly-L-lysine/casein multilayers

The aim of our work was to investigate formation of multilayer films containing biocompatible polycation poly-L-lysine (PLL) and α- or β-casein. Since in the neutral pH casein is negatively charged, it has been used as a polyanionic layer for the film build-up. Casein containing films were formed at surface of Si/SiO2 wafers and their thickness was measured by ellipsometry. The effect of ionic strength of PLL and casein solutions was investigated. After the multilayer films were formed, they were contacted with solutions having various pH and salts to determine film stability under these conditions. Additionally the response of the thickness of PLL/casein films to the temperature variation in the range of 5–45 °C was also analyzed. Formation and stability of casein containing films was also investigated on surfaces of titanium and stainless steel. We used fluorescently labeled protein to monitor the amount of casein in the film and its change after treatment with solutions containing calcium ions.