Structure and morphology of adsorbed protein (BSA) layer on hydrophilic silicon surface in presence of mono-, di- and tri-valent ions

Abstract

Out-of-plane structure and surface morphology of the adsorbed thin films of globular protein bovine serum albumin (BSA) are investigated using X-ray reflectivity (XRR) and atomic force microscopy (AFM). BSA adsorption on hydrophilic silicon surface is done by dip coating method in absence and presence of mono- (Na + ), di- (Ca 2+ ) and tri- (La 3+ and Y 3+ ) valent ions in BSA solution for different salt concentrations. Unlike mono- and di-valent ions, BSA shows re-entrant phase transition for tri-valent ions like La 3+ and Y 3+ with their concentration variation. XRR study shows that the thickness of the adsorbed BSA layer slightly increases with the increase of mono- and di-valent ions concentration, while for tri-valent ions, considerable amount of thickness is obtained when the film is deposited from the condensed phase under re-entrant condensation and becomes relatively less with salt concentrations lower or higher than that particular salt concentration, however, thickness is again increased for higher salt concentration. Surface morphologies of the films are also modified with the variation of the salt type and their concentration. Thus, structural and morphological changes of the adsorbed protein layer on hydrophilic surface and the probable reason for such modifications are explored in the presence of different valent ions with their concentration variation. • BSA adsorption on hydrophilic surface is done in absence/presence of ions. • In presence of mono- and di-valent ions, bilayer-like structure is formed. • For tri-valent ions, concentration dependent structures are formed. • At turbid phase, tilted molecules are shifted vertically to form a trilayer-like structure. • Surface morphologies of adsorbed BSA films depend on salt type and concentration.