Quantitative analysis of albumin adsorption onto uncoated and poly(ether)urethane-coated ZnSe surfaces using the attenuated total reflection FTIR technique

An attenuated total reflection (ATR) Fourier transform infrared radiation (FTIR) technique has been explored for the in situ quantitative analysis of bovine serum albumin (BSA) adsorption from aqueous solutions onto a segmented poly(ether)urethane film deposited on a ZnSe internal reflection element (IRE) and onto a bare ZnSe IRE surface. The IR spectral area of the amide II band was used for the quantitative analysis of adsorption. BSA adsorption reached equilibrium within 30 min and changed linearly with solution concentration in the range 0.5-6 wt.% and was found to be dependent on the solution pH and substrate type. At the physiological concentration, BSA adsorption densities of 2.4 mg cm^-2 and 3.9 μg cm^-2 were obtained for ZnSe and polyurethane respectively. The adsorption density was higher at pH 7 than that at pH 3 or 11, and both α-helix and β-sheet structures were present in the adsorbed layer. BSA adsorbed onto these solids appears to adopt an extended conformation and the long axis of the molecule appears to lie in the plane of the interface. Adsorption density was higher on the more hydrophobic polyurethane surface than on the relatively less hydrophobic ZnSe crystal surface.