Bovine serum albumin adsorption on SiO2 and TiO2 nanoparticle surfaces at circumneutral and acidic pH: A tale of two nano-bio surface interactions.

The interaction of a model protein, bovine serum albumin (BSA) with two different metal oxide nanoparticles, TiO2 (∼22nm) and SiO2 (∼14nm), was studied at both physiological and acidic pH. The pH- and nanoparticle-dependent differences in protein structure and protein adsorption were determined using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA). The results indicated that the surface coverage of BSA decreases with decreasing pH on both TiO2 and SiO2 surfaces, and BSA coverage is higher by a factor of ca. 3-10times more on TiO2 compared to SiO2. The secondary structure of BSA changes upon adsorption to either nanoparticle surface at both pH 7.4 and 2. At acidic pH, BSA appears to completely unfold on TiO2 nanoparticles whereas it assumes an extended conformation on SiO2. These differences highlight for the first time the extent to which the protein corona structure is significantly impacted by protein-nanoparticle interactions which depend on the interplay between pH and specific nanoparticle surface chemistry.