Self-Assembled Monolayers of Methyl 1-Thiahexa(ethylene oxide) for the Inhibition of Protein Adsorption

Self-assembled monolayers (SAMs) of methyl 1-thiahexa(ethylene oxide), HS(CH2CH2O)6CH3, on gold with different molecular conformations were evaluated for their ability to inhibit protein adsorption. Assembled from 95% ethanol, reflection−absorption infrared spectroscopy (RAIRS) data show that the HS(CH2CH2O)6CH3 SAMs adopt the well-ordered 7/2 helical conformation of the folded-chain crystal polymorph of poly(ethylene oxide). Electrochemical impedance spectroscopy (EIS) data indicate that these ordered helical SAMs behave as near ideal capacitors in an electrochemical environment. Assembled from other solvents, the SAMs of HS(CH2CH2O)6CH3 were more variable and less ordered. For samples assembled from 100% ethanol, the RAIRS data were virtually identical to those obtained from 95% ethanol indicating the predominant 7/2 helical structure but the EIS spectra show consistently higher specific capacitance values indicating a slight increase in disorder or number of defect sites. In contrast to the ethanolic solvents, assembled from tetrahydrofuran, the HS(CH2CH2O)6CH3 SAMs are significantly less ordered with RAIRS data clearly showing mixtures of the 7/2 helical and nonhelical conformations and EIS data showing much higher specific capacitance values. Exposure of these ordered and disordered HS(CH2CH2O)6CH3 SAMs to bovine serum albumin and lysozyme solutions showed that the less ordered SAMs exhibit better inhibition of protein adsorption.