The ability of Keggin-type phosphododecamolybdate (PMo12O403-PMo12) to undergo chemisorption on solid surfaces (including gold) is explored here to convert (by ligand place-exchange and phase transfer to aqueous solution) the alkanothiolate-modified Au nanoparticles of controlled size (prepared in toluene) into a stable colloidal solution Of PMo12-protected gold nanoparticles, PMo12-AuNPs, the sizes of which are ca.4-5 nm as determined by transmission electron microscopy. By dip-coating, PMo12-AuNPs were assembled on carbon electrode substrates. The step-by-step assembly, by which alternate exposures to the solutions of PMo12-AuNPs and either anilinium cations or pyrrole monomers, was utilized to grow in controlled manner hybrid network films in which the negatively charged PMo12-AuNP deposits were linked, or electrostatically attracted, by ultra-thin, positively charged conducting polymer (polyaniline or polypyrrole) structures. The three-dimensionally distributed PMo12-AuNPs immobilized within the polypyrrole-based composite film exhibited some electrocatalytic reactivity towards reduction of hydrogen peroxide. (c) 2007 Elsevier Ltd. All rights reserved.