Adsorption of human serum albumin on electrochemical titanium dioxide electrodes: Protein–oxide surface interaction effects studied by electrochemical techniques

The adsorption of Human Serum Albumin (HSA) on a semiconductor TiO2 electrochemical oxide was investigated using Cyclic Voltammetry (CV), Capacity–Potential curves (C–E) and time-resolved techniques as a function of electrode potential and protein concentration. The presence of HSA adsorbed on the electrode surface modifies the voltamperometric behavior of the hydrogen evolution reaction (her) and also produces a major modification in the diffusional layer thickness of the H+ ions. The adsorbed amounts of HSA were analyzed throughout different adsorption isotherms. The experimental data were modeled with a modified Langmuir type isotherm, considering a weak chemisorption on a surface with heterogeneity in site-energy distribution with some degree of attractive lateral interactions between the adsorbed protein molecules. The effect of the adsorption potential (Eads) was investigated polarizing the electrode at −0.70, −0.50 and −0.08 V vs. SCE. The capacity response obtained from the different impedance experiments was determined by the space charge region in the semiconductor. It was possible to correlate processes produced by the protein adsorption on the surface (occurring in the electrolyte side of the interface) with changes in the semiconductor properties of the TiO2 (in the oxide side of the interface). The adsorption of HSA produces an increase in donor concentration (ND) of the semiconductor and a shift of the Efb to more negative values. These effects are more pronounced with an increase in the protein concentration. The relative change in ND is lower and the change in Efb is higher when the adsorption occurs at less negative applied potentials. Adsorption kinetics and thermodynamic parameters were calculated for a wide protein concentration range.