Ellipsometric study of bovine serum albumin adsorbed onto Ti/TiO2 electrodes

The adsorption of bovine serum albumin (BSA) onto relatively hydrophobic Ti O2 surfaces was studied by ellipsometry as a function of pH and BSA concent ration. Titanium oxide layers were electrochemically grown on Ti disc elect rodes. When fast attachment of BSA onto TiO2 takes place, the adsorption ca n be considered as occurring in two different steps. The first step is fast and is the result of the direct adsorption of the protein molecules that a ttach to the surface without changing their conformation. The second proces s is slow and lasts for several hours. In this process, the adsorbed amount remains constant, whereas the thickness of the layer increases and its ref ractive index decreases with time. The changes in this second step are due mainly to rearrangements in the adsorbed layer produced by variations in th e conformation and structure of the adsorbed molecules, The main conformati onal changes take place in the direction normal to the surface because late ral molecule-molecule interactions impede significant lateral expansion. Ad sorption from BSA solutions of low concentration does not appear to lead to significant reconformation of the protein layer. Comparison with adsorptio n on powdered TiO2 indicates that the adsorbed amount and the effective are a occupied by an adsorbed BSA molecule can remain about constant even when strong surface reconformation takes place. (C) 1999 Academic Press.