Electrochemical studies of the adsorption behavior of serum proteins on titanium

Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were us ed to examine the adsorption behavior of bovine serum albumin (BSA) and bov ine fibrinogen on titanium in phosphate buffer pH 7.4, over the temperature range 295-343 K. It was shown that the surface charge density is directly proportional to the amount of the adsorbed protein (surface concentration), thus indicating that the adsorption is accompanied by the transfer of char ge, i.e. chemisorption. On the other hand, the resulting adsorption pseudoc apacitance obtained under the potentiostatic conditions not only depends on the protein surface concentration but also is a very complex function of p arameters that are, in turn, dependent on structural, physical, and chemica l properties of the proteins. Both techniques were shown to be very sensiti ve to the conformational behavior of the proteins. The adsorption of BSA on to a Ti surface resulted in a bimodal isotherm at all the temperatures stud ied, while the adsorption of fibrinogen resulted in a single saturation pla teau. The adsorption process was modeled with a Langmuir adsorption isother m. It was found that fibrinogen exhibits more than twice the affinity for a dsorption onto a Ti surface compared to BSA. At lower surface coverage, ads orption appears to be mainly surface binding rate limited. The calculated s tandard Gibbs energies of adsorption also suggested a very strong adsorptio n of both proteins through a chemisorption process. The adsorption process for both proteins was found to be endothermic, resulting from the excess en ergetics required for the disruption of intramolecular interactions relativ e to those involved in the formation of protein-metal interactions, i.e. ch emisorption at the electrode surface. In addition, adsorption of BSA onto a Ti surface at low concentrations was shown to be an entropically controlle d process, also suggesting structural unfolding of the protein occurs at th e electrode surface.