Adsorption and photocatalytic degradation of human serum albumin on TiO2 and Ag-TiO2 films

Titanium dioxide is a useful material in the biomedical field as it has excellent biocompatibility based on its non-toxicity and non-inflammatory properties. Furthermore, TiO2 can be excited by UV light to create charge carriers giving rise to photocatalytic redox reactions at the surface and photo-induced super-hydrophilicity. These properties might be exploited for surface decontamination of medical devices and implants. With this in mind, titanium dioxide TiO2 films were prepared on stainless steel substrates using magnetron sputtering. Silver loaded (Ag-TiO2) films were prepared by the photocatalytic reduction of Ag+ from solution. The adsorption of human serum albumin (HSA) was studied. Surface analysis methods used included X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy and atomic force microscopy (AFM). The TiO2 films were predominantly anatase crystal phase and the photoreduced Ag was present at greater than 90% of the silver content as Ag-0 on the surface. Ag loading of the TiO2 markedly enhanced the Raman signal (ca. 15-fold), but caused significant changes to the spectrum indicating non-specific binding of protein side chain residues to the Ag. The amide I and Ill modes remained well-resolved and were used to estimate the conformational change induced by the Ag. Raman analysis showed an increase in the intensity of the band at similar to 1665 cm(-1) assigned to the disordered conformation, suggesting that the adsorption to the Ag sites induces conformational changes in the protein. UVB irradiation of the protein contaminated surfaces caused further changes in the protein conformation, consistent with denaturation and enhanced binding and oxidation, thought to be induced through a photocatalytic mechanism. (C) 2011 Elsevier B.V. All rights reserved.