Adsorption of Proteins onto Surfaces Containing End-Attached Oligo( ethylene oxide): A Model System Using Self-Assembled Monolayers

This paper reports a study of the adsorption of four proteins-fibrinogen, lysozyme, pyruvate kinase, and RNAse A-to self-assembled monolayers (SAMs) on gold. The SAMs examined were derived from thiols of the structure HS(CH2)loR, where R was CH3, CHzOH, and oligo(ethy1eneoxide). Monolayers that contained a sufficiently large mole fraction of alkanethiolate groups terminated in oligo(ethy1eneoxide) chains resisted the kinetically irreversible, nonspecific adsorption of all four proteins. Longer chains of oligo(ethy1ene oxide) were resistant at lower mole fractions in the monolayer. Resistance to the adsorption of proteins increased with the length of the oligo(ethy1ene oxide) chain: the smallest mole fraction of chains that prevented adsorption was proportional to where n represents the number of ethylene oxide units per chain. Termination of the oligo(ethy1ene oxide) chains with a methoxy group instead of a hydroxyl group had little or no effect on the amount of protein adsorbed. The amount of pyruvate kinase that adsorbed to mixed SAMs containing hexa(ethy1ene oxide)-terminated chains depended upon the temperature. When the mole fraction of oligo(ethy1ene oxide) groups in the monolayer was below the level needed to prevent adsorption, more pyruvate kinase adsorbed to the monolayer at 37 "C than at 25 "C. No difference was observed between adsorption at 25 and 4 "C.