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 usin g (aminopropyl)siloxane or (mercaptopropyl)siloxane as base monolayer for the deposition of the metal colloid. Different Au colloids, rangin g in particles of diameters 25, 30, 35, and 120 nm, were deposited on the monolayer-modified ITO surfaces. For the small particles, 25 nm, a n almost continuous Au colloid film is formed with interparticle spaci ng of 10-25 nm. The surface coverage of the Au colloid on the (aminopr opyl)siloxane monolayer is higher than that for the (mercaptopropyl)si loxane-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 monol ayer assembled onto the Au colloids. For the 25-nm Au colloid the surf ace coverage by the redox active unit, 6.8 x 10(-10) mol cm(-2), is ca . 12-fold higher than that of the (aminopropyl)siloxane monolayer-modi fied ITO, lacking the Au film. The surface coverages of the Au colloid films by the bipyridinium monolayers increase as the colloid particle sizes decrease.