Effect of different valent ions (Na+, Ca2+ & Y3+) on structural and morphological features of protein (BSA) thin films adsorbed on hydrophobic silicon (H-Si) surface

Abstract

Structure and morphology of bovine serum albumin (BSA) films adsorbed on hydrophobic silicon (H-Si) surface from BSA solution in presence of different cationic ions (Na+, Ca2+ and Y3+) are studied. Electron density profile as obtained from X-ray reflectivity analysis shows that ≈ 55 Å thick monolayer of pure BSA is adsorbed on H-Si surface, while atomic force microscopy image displays its globular morphology. A bilayer of globular BSA molecules of average thickness ≈ 85 Å is formed on the H-Si surface at 1–10 mM of Na+ and Ca2+ ions. However, Y3+ ions favor the immobilization of a tri-layer of BSA on H-Si surface except for 5 mM, at which a tetralayer is formed due to the effect of re-entrant condensation of BSA solution. Elemental mapping analysis as obtained from scanning electron microscopy confirms that the attachment of Y3+ ions is higher in comparison with Na+ and Ca2+ ions due to maximum charge density of hydrated Y3+ ions. The contact angle results display intermediate hydrophobicity for Na+ ions, whereas minimum and maximum hydrophobicity for Ca2+ and Y3+ ions interacted protein films, respectively. It is found that the adsorption of BSA is relatively higher in presence of all ions on hydrophobic surface than hydrophilic. All the adsorbed BSA films are found mostly stable with time.