Sequential adsorption of γ-interferon and bovine serum albumin on hydrophobic silicon surfaces

Abstract

The adsorption and exchange of proteins, γ-interferon and bovine serum albumin, on a silicon surface modified by dimethyldichlorosilane have been studied by ellipsometry and radioactive labeling. It was found that both proteins were adsorbed reversibly according to the Langmuir model. BSA was adsorbed from 0.01 M phosphate buffer (pH = 7.2) containing 0.1 M NaCl on the hydrophilic and hydrophobic silicon surfaces. Hydrophobization of the silicon surface resulted in a 58-fold increase and a 27-fold decrease of the adsorption and desorption rate constants, respectively, as compared with the appropriate rate constants of a hydrophilic surface. The maximal surface concentrations of BSA in the same buffer evaluated on the hydrophilic (1.18 mg/m 2) and hydrophobic (0.89 mg/m 2) silicon surfaces indicated considerable conformation changes in the protein molecules on the surfaces. Studies on the displacement degree of γ-INF from the hydrophobic silicon surface by the BSA molecules revealed that it varied between 32–34% and 59% with the addition of 0.14 M NaCl and 0.01 M KCl to 0.01 M of the phosphate buffer solution. Moreover, the nonionic detergent Tween-20 completely displaced the protein on the surface. This indicates an electrostatic interaction between γ-INF and BSA. Electrostatic interaction between γ-INF on the surface and BSA in the solution may be prevented if the γ-INF layer is formed from the alkaline solution at pH 9.5. In this case the displacement degree is increased to 83%.