A high-density poly(ethylene glycol) polymer brush for immobilization on glass-type surfaces

Label-free heterogeneous phase detection critically depends on the properti es of the interfacial layer. We have obtained high-density monomolecular po ly(ethylene glycol) (PEG) layers by solvent-free coupling of homo-bifunctio nal PEGs (2000 g/mol) at 75 degreesC to silica surfaces silanized with glyc idyloxipropyltrimethoxysilane (GOPTS). Characterization by ellipsometry and contact angles revealed that PEG layers up to 3.4 ng/mm(2) with low roughn ess and flexibility were obtained. Specific and non-specific binding at the se PEG surfaces was monitored by reflectometric interference spectroscopy ( RIfS). No significant non-specific adsorption upon incubation of 1 mg/ml ov albumin was detectable (< 10 pg/mm(2)), and 150 pg/mm(2) upon incubation of 10% calf serum, less than 10% of the amount adsorbed to the sorely silaniz ed surfaces. The terminal functional groups of the PEG layers were utilized to couple ligands and a protein. Specific protein interaction with these i mmobilized compounds was detected with saturation loadings in the range of protein monolayers (2-4 ng/mm(2)). The excellent functional properties, the high stability of the layers, the generic and practical coupling procedure and the versatility for immobilizing compounds of very different functiona lity make these PEG layers very attractive for application in label-free de tection with silica or metal-oxide based transducers. (C) 2000 Elsevier Sci ence S.A. All rights reserved.