Role of interfacial water on protein adsorption at cross-linked polyethylene oxide interfaces.

Sum frequency generation (SFG) vibrational spectroscopy was used to study the structure of water at cross-linked PEO film interfaces in the presence of human serum albumin (HSA) protein. Although PEO is charge neutral, the PEO film/water interface exhibited an SFG signal of water similar to that of a highly charged water/silica interface, signifying the presence of ordered water. Ordered water molecules were observed not only at the water/PEO interface, but also within the PEO film. It indicates that the PEO and water form an ordered hydrogen-bonded network extending from the bulk PEO film into liquid water, which can provide an energy barrier for protein adsorption. Upon exposure to the protein solution, the SFG spectra of water at the water/PEO interface remained nearly unperturbed. For comparison, the SFG spectra of water/silica and water/polystyrene interfaces were also studied with and without HSA in the solution. The SFG spectra of the interfacial water were correlated with the amount of protein adsorbed on the surfaces using fluorescence microscopy, which showed that the amount of protein adsorbed on the PEO film was about 10 times less than that on a polystyrene film and 3 times less than that on silica.