Adsorption of HSA on Ti/TiO2 electrochemical oxide electrodes. Quantitative interaction effects of protein-oxide surface functional groups

F. Y. OLIVA, L.B. AVALLE , O.R.CÁMARA

Sevilla, España

Congreso; 59th Annual Meeting of the International Society of Electrochemistry (ISE); 2008

International Society of Electrochemiostry (ISE)

<!-- @page { size: 8.5in 11in; margin: 0.79in } P { margin-bottom: 0.08in } --> The adsorption of HSA onto Ti/TiO2 electrodes and its effect on the state of the electrode surface have been investigated in 0.1 M NaCl at pH 4.7 at different adsorption potentialsby Cyclic Voltammetry, Electrochemical Impedance Spectroscopy, and time resolved techniques. The titanium oxide (~ 8 nm) was potentiodinamicaly grown and the adsorption of HSA adsorption was studied as a function of time, protein concentration in the bulk solution and electrode potentials  -0.7, -0.5, -0.08 V, above and below the TiO2 flat band potential (Vfb ~ -0.5V) The capacitance and voltammetric charge measurements obtained for one step or for multistep addition of protein aliquots into the electrochemical cell, shown that the physicochemical properties of the adlayer formed on the surface of the electrode approach to different final steady states. In the -0.7 to -0.4 V vs SCE electrode potential range, the changes observed in capacitance upon protein addition could be associated to surface state generation, while in the -0.4 to 1 V range the predominant effect observed in potentiodynamic profiles is the inhibition of charge transfer reactions by protein adlayer. In order to analyze the observed capacity-time dependence for increasing values of protein concentration in solution, the raw experimental data for each protein concentration were fitted with different mathematical functions in two time domains, above and below 300 s showing different kinetics behaviour.The calculations obtained using a Mott-Schotky approach demonstrate that there is a correlation between the increasing protein concentration present into the bulk of the solution and the flat band potential shifting toward more negative potentials. The donor concentration of the electrode calculated in steady state conditions remains constant for all concentrations of protein in solution, evidencing that the effect exert by the protein is mainly determined by the physicochemical nature of the protein-oxide interactions that generate suface states more than the concentration of such states. The differences observed in cathodic and anodic charge values after protein adsorption as a function of v−1/2 demonstrate that the involved processes are not only related to proton ion transport and reduction/ oxidation of the inner redox couple reactions, but could also be correlated with an exchange mechanism that involves protein and oxide surface acid-basic groups which is controlled by a diffusional step.