Protein-resistant coatings for glass and metal oxide surfaces derived from oligo(ethylene glycol)-terminated alkyltrichlorosilanes

This paper describes the preparation of oligo(ethylene glycol)-terminated alkyltrichlorosilanes, Cl3Si(CH2)11(OCH2CH2)nOCH3 (n=2, 3), and their use in the formation of self-assembled monolayers on an oxide surface. The adsorption of the trichlorosilanes from solution produces densely packed, oriented monolayer films that are 2–3 nm in thickness. The trichlorosilyl group anchors the molecules to the surface, and the resulting film exposes the ethylene glycol units at its surface, as noted by its moderate hydrophilicity (θa(H2O)≈68°). The films are robust with stabilities similar to those of other alkylsiloxane coatings. These oligo(ethylene glycol)-terminated silane reagents produce films that notably exhibit resistances against the non-specific adsorption of proteins from solution that are better than for films prepared from octadecyltrichlorosilane. With insulin, lysozyme, albumin, and hexokinase, no adsorption was observed with the oligo(ethylene glycol)-siloxane coatings whereas protein films of approximately a monolayer formed on surfaces-treated with octadecyltrichlorosilane. With fibrinogen, complete resistance was not possible with either coating; however, the oligo(ethylene glycol)-siloxane coatings exhibited greater resistance against non-specific adsorption. The oligo(ethylene glycol)-siloxane coatings offer performance advantages over available systems and could easily provide a direct and superior replacement in protocols that presently use silane reagents to generate hydrophobic, ‘inert’ surfaces.