In Situ Control of the Oxide Layer on Thermally Evaporated Titanium and Lysozyme Adsorption by Means of Electrochemical Quartz with Dissipation

Journal article, 2009

Electrochemical (EC) quartz crystal microbalance with dissipation monitoring (ECQCM-D) is a new and powerful technique for the in situ study of adsorption phenomena. e.g., as a function of the potential of the substrate. When titanium Ti) is employed as the substrate, its oxidation behavior needs to be taken into account. Ti is always covered with a native oxide layer that can grow by, e.g., thermal oxidation or under anodic polarization. For biomolecular adsorption studies on oxidized Ti under applied potential, a stable oxide layer is desired in order to be able to distinguish the adsorption studies on oxidized Ti under applied potenital, a stable oxide layer is desired in order to be able to distinguish the adsorption phenomena and the oxide growth. Therefore, the oxidation of thermally evaporated Ti films was investigated in phosphate buffered saline by means of ECOCM-d, using a specially designed EC flow cell Upon stepping the potential applied to Ti up to 2.6 V vs standard hydrogen electrode (SHE), a fast increase of the mass was observed initially for each potential step evolving slowly to an asymptotic mass change after several hours. The oxide layer thickness increased as a quasi-linear function of the oxidation potential for potential up to 1.8 V vs SHE. The composition of the oxide layer was analyzed by X-ray photoelectron spectroscopy (XPS) it was mainly composed of TiO2 with a small percentage of suboxides (TiO and Ti2O3) primarily at the inner metal/oxide interface. The amount composed of TiO2, with a small percentage of suboxides TiO and Ti2O3 decreased with increasing oxidation potential. For each oxidation potential the calculated thickness obtained from ECQCM-D correlated well with the thickness obtained by XPS depth profiling. A procedure to prepare Ti samples with a stable oxide layer was successfully established for investigations on the influence of an electric field on the adsorption of biomolecules. As such, the effect of an applied potential on the adsorption behavior of lysozyme on oxidized Ti was investigated. It was observed that the adsorption of lysozyme on oxidized Ti was not influnced by the applied potential.