Organization of Au Colloids as Monolayer Films onto ITO Glass Surfaces: Application of the Metal Colloid Films as Base Interfaces To Construct Redox-Active Monolayers

Au colloid films are organized on indium tin oxide (ITO) surfaces using (aminopropyl)siloxane or (mercaptopropyl)siloxane as base monolayer for the deposition of the metal colloid. Different Au colloids, ranging in particles of diameters 25, 30, 35, and 120 nm, were deposited on the monolayer-modified ITO surfaces. For the small particles, 25 nm, an almost continuous Au colloid film is formed with interparticle spacing of 10-25 nm. The surface coverage of the Au colloid on the (aminopropyl)siloxane monolayer is higher than that for the (mercaptopropyl)siloxane-modified ITO. The Au colloid films provide active surfaces for the self-assembly of redox-active thiolate monolayers. 8-(N-Methyl-4,4'-bipyridinyl)octanoic acid was covalently linked to a cystamine monolayer assembled onto the Au colloids. For the 25-nm Au colloid the surface coverage by the redox active unit, 6.8×10 -10 mol-cm -2 , is ca. 12-fold higher than that of the (aminopropyl)siloxane monolayer-modified ITO, lacking the Au film. The surface coverages of the Au colloid films by the bipyridinium monolayers increase as the colloid particle sizes decrease