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

The adsorption of bovine serum albumin (BSA) onto relatively hydrophobic TiO2 surfaces was studied by ellipsometry as a function of pH and BSA concentration. Titanium oxide layers were electrochemically grown on Ti disc electrodes. When fast attachment of BSA onto TiO2 takes place, the adsorption can 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 attach to the surface without changing their conformation. The second process is slow and lasts for several hours. In this process, the adsorbed amount remains constant, whereas the thickness of the layer increases and its refractive index decreases with time. The changes in this second step are due mainly to rearrangements in the adsorbed layer produced by variations in the conformation and structure of the adsorbed molecules, The main conformational changes take place in the direction normal to the surface because lateral molecule-molecule interactions impede significant lateral expansion. Adsorption from BSA solutions of low concentration does not appear to lead to significant reconformation of the protein layer. Comparison with adsorption on powdered TiO2 indicates that the adsorbed amount and the effective area occupied by an adsorbed BSA molecule can remain about constant even when strong surface reconformation takes place. (C) 1999 Academic Press.