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The adsorption behavior of bovine serum albumin (BSA) on high-purity austenitic low-carbon stainless steel and its effect on the state of the electrode surface have been studied over the temperature range 299-343 K under open-circuit-potential conditions, using electrochemical impedance spectroscopy (EIS). The impedance spectra were interpreted in terms of an equivalent electrical circuit (EEC) based on a possible physical model with the circuit elements representing the electrochemical properties of the investigated system. The adsorption of BSA onto the stainless steel surface resulted in an increased rate of metal dissolution, i.e., corrosion. The plateau values of corrosion rate were achieved after a "threshold" BSA concentration in the bulk solution at all the temperatures studied. The rate of the corrosion process was found to be controlled by both the surface diffusion and charge transfer process. Adsorption of BSA onto the stainless steel surface was described with a Langmuir adsorption isotherm. The thermodynamic data were calculated to give the corrosion activation energy, Gibbs free energy, enthalpy, and entropy of adsorption. The data suggested a very strong adsorption of BSA molecules, accompanied by a charge transfer mechanism involving chemisorption. An adsorption mechanism was proposed involving the interaction of the negatively charged carboxylate groups of the proteins with the stainless steel surface. The EIS technique was shown to be a valuable tool in studying the interfacial behavior of proteins at metal electrode surfaces.

Cyclic voltammetry and electrochemical impedance spectroscopy (EIS) were used to examine the adsorption behavior of bovine serum albumin (BSA) and bovine 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 charge, i.e. chemisorption. On the other hand, the resulting adsorption pseudocapacitance obtained under the potentiostatic conditions not only depends on the protein surface concentration but also is a very complex function of parameters that are, in turn, dependent on structural, physical, and chemical properties of the proteins. Both techniques were shown to be very sensitive to the conformational behavior of the proteins. The adsorption of BSA onto a Ti surface resulted in a bimodal isotherm at all the temperatures studied, while the adsorption of fibrinogen resulted in a single saturation plateau. The adsorption process was modeled with a Langmuir adsorption isotherm. It was found that fibrinogen exhibits more than twice the affinity for adsorption onto a Ti surface compared to BSA. At lower surface coverage, adsorption appears to be mainly surface binding rate limited. The calculated standard Gibbs energies of adsorption also suggested a very strong adsorption of both proteins through a chemisorption process. The adsorption process for both proteins was found to be endothermic, resulting from the excess energetics required for the disruption of intramolecular interactions relative to those involved in the formation of protein-metal interactions, i.e. chemisorption at the electrode surface. In addition, adsorption of BSA onto a Ti surface at low concentrations was shown to be an entropically controlled process, also suggesting structural unfolding of the protein occurs at the electrode surface.

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