Effect of pH on the Adsorption of Bovine Serum Albumin at the Silica/Water Interface Studied by Neutron Reflection

Abstract

In a previous study of BSA adsorption onto the hydrophilic silica/water interface using neutron reflection, we examined the concentration dependence of the surface excess of BSA at a pH close to its isoelectric point (IP). The surface excess was found to reach a plateau at a very low bulk protein concentration, suggesting a high affinity of BSA for the oxide surface. This work has now been extended to an investigation of the structure and composition of the BSA layer above and below its IP. It is found that adsorption of BSA is strongly dependent on pH, although the protein concentration has little influence on the surface excess at pH 3 and 7. Changing the pH from the IP substantially reduces the surface excess. The structure of the adsorbed layers below a bulk BSA concentration of 0.5 g dm-3 can be fitted to a single uniform layer distribution over all pH conditions studied, which suggests that there is no significant denaturation. Denaturation generally leads to a more fragmented peptide distribution a...