Bovine Serum Albumin Adsorption on TiO2 Nanoparticle Surfaces: Effects of pH and Coadsorption of Phosphate on Protein-Surface Interactions and Protein Structure

Protein adsorption on nanoparticle surfaces plays a critical role in biological systems, and bovine serum albumin (BSA) is a useful model protein to study due to its high abundance and, similar properties as its human variant. Herein, a quantitative understanding of the interaction between titanium dioxide (TiO2) nanoparticle (22 nm average diameter) and BSA was carried out to explore the effect of pH on surface coverage and adsorbed protein structure. Experiments were conducted under different pH conditions (pH 7.4, 4.5, and 2.0) that simulate the pH of blood, lung, and stomach fluids,, respectively. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy was used for in situ adsorption characterization and protein secondary structure analysis. In addition, thermogravimetric analysis (TGA) was used to provide quantitative determination of the surface coverage. These results show that BSA adsorption on TiO2 highly depends on pH as well as the presence of salts. Furthermore, it is also shown that coadsorbed phosphate ion reduces the amount denaturation of BSA on TiO2 at acidic pH. Thus, the results of this study provide new insights into understanding protein behavior on nanoparticle surfaces at different pH in the presence and absence of coadsorbed phosphate.