Temperature dependence of the protein resistance of poly- and oligo(ethylene glycol)-terminated alkanethiolate monolayers

Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) has been used to study the protein resistance of poly- and oligo(ethylene glycol) (PEG and OEG) terminated alkanethiolate self-assembled monolayers (SAMs) on Au and Ag in the temperature range from 0 to 85 degreesC. These experiments extend previous room-temperature studies by Harder et al. I who related the protein adsorption characteristics of OEG-SAMs to the lateral density and corresponding molecular conformation of the ethylene glycol (EG) moieties in the film. In addition to the short oligomer OEG-SAMs, we investigated PEG-derivatized alkanethiolate monolayers with an average chain length of 45 EG units and a mean molecular mass of 2000 g/mol (PEG2000). We observe that films, which are protein resistant at room temperature, maintain their protein repulsive characteristics up to 85 degreesC but may adsorb significant amounts of protein if the temperature is lowered.