BOVINE SERUM-ALBUMIN ADSORPTION TO MICA SURFACES

Bovine serum albumin (BSA) has been adsorbed onto mica surfaces and studied in two ways. By using energy-resolved X-ray photoelectron spectroscopy (XPS), i.e. using X-rays of different wavelengths, it was possible to determine that 4.5 +/- 1.0 mg m-2 of protein adsorbed. The forces of interaction between the mica surfaces bearing an adsorbed layer of BSA at pH 5.5 revealed that at long range the forces were dominated by electrical double layer forces, whilst at surface separations of around 30 nm a steric component due to the protein was noted and the surfaces could be compressed to a separation of 18-20 nm. No attractive or adhesive forces were observed. At a pH of 3.5, the steric component to the force could not be detected and the surfaces could approach to 12 nm from mica-mica contact. These results are explained in terms of a conformational change of BSA at the lower pH, as is indicated by earlier adsorption studies on polystyrene latex.