Adsorption and thermal properties of the bovine serum albumin-silicon dioxide system

Abstract

The adsorption, electrokinetic, thermal and stability properties of the silicon dioxide (silica, SiO 2)/bovine serum albumin (BSA) system were determined. All measurements were carried out as a function of solution pH value. The highest amount of BSA absorbed on the silica surface was observed at pH 4.6 [the value close to the BSA isoelectric point (pI)], which is primarily related to the packed albumin conformation and the lack of adsorbent-adsorbate electrostatic repulsion. At pH 4.6, largest mass decrease was also noticed (thermogravimetric measurements). At pH 3, 7.6 and 9, the adsorption levels were much lower. This phenomenon is associated with the electrostatic repulsion between the BSA macromolecules and the silica particles as well as the expanded BSA structure. During biopolymer adsorption, the whole solid surface is coated with the albumin macromolecules. Then, the properties of the silica particles become similar to those of the BSA macromolecules. In the presence of albumin, the silica pH iep point is identical to the BSA pI value. It should also be noted that the albumin adsorption affects the SiO 2 suspension stability. The greatest change was observed at pH 3. Under these conditions, the BSA addition causes electrosteric system stabilization.