We report our efforts to understand the passivation behavior of bovine serum albumin (BSA) and its structural changes at interfaces using X-ray photoelectron spectroscopy and contact angle measurements. The work investigated protein adsorption on two surfaces with widely different surface free energies. We investigated a hydrophilic surface represented by clean glass and a hydrophobic surface prepared by modifying a glass surface with a fluorinated self-assembled monolayer. The experiments indicate that, on the hydrophilic surface, BSA adsorbs in a two-step process and passivation of the surface is reached. Adsorption of BSA on the hydrophobic surface also continues until passivation of the surface. In contrast, however, the process occurs in a single step. Contact angle measurements show that at the completion of the adsorption process in both cases the same contact angle is reached despite the different adsorption behavior. We believe that this strongly indicates that the same outer surface composition is obtained for both surfaces despite different passivation routes. We postulate that there is a controlled loss of tertiary structure of BSA in descrete units that allows a specific structure to be formed on the surface that inhibits further protein adsorption regardless of the initial surface composition.
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