The aim of this Study was the immobilization of COOH-modified poly(ethylene glycol) (PEG) layers onto beta-cyclodextrin-coated surfaces by formation of inclusion complexes, in view of biosensors applications. To this end, PEGs with one phenyladamantyl and one carboxylic end group (Ad-PEG-COOH) were prepared according to a three-step procedure. After modification of PEG with 4-toluenesulfonylchloride, the reaction of the tosyl intermediate with the alcoholate of 4-(1-adarnantyl)-phenol was carried Out in tetrahydrofuran to avoid the formation of by-products. Then, it was shown by high performance liquid chromatography that the association between beta-cyclodextrin cavities and Ad-PEG-COOH polymers was not hindered by the presence of the COOH group. Last, the Ad-PEG-COOH polymer was immobilized onto beta-cyclodextrin-coated gold surfaces by formation Of inclusion complexes. The immobilization was performed in water, at room temperature, with a rapid kinetics. After activation of COOH groups with N-hydroxysuccinimide, beta-lactoglobulin was coupled to the biocompatible PEG layer. Functionalization of the gold surface with beta-cyclodextrin cavities, immobilization of Ad-PEG-COOH onto the surface, and coupling of the protein to the reactive PEG layer were followed in real time by surface plasmon resonance imaging system. (c) 2006 Wiley Periodicals, Inc.