Sequential layer-by-layer growth of Au nanoclusters protected by a mixed self-assembled monolayer with a polymer binding layer – Effects of pH and ionic strength of the polymer solution

Amounts of gold nanoclusters (GNCs) in multilayer assembly with polymer binding layers has been demonstrated to be controlled by pH and ionic strength of the polymer solution when GNCs covered with mercaptoundecanoic acid (MUA) were assembled on a solid substrate in a layer-by-layer (LBL) fashion utilizing terminal carboxylate groups as charged sites to electrostatically bind to protonated amine groups of poly(allylamine hydrochloride) (PAH), which was used as a binding layer. Formation of these GNC multilayers was followed by monitoring the electrochemical response of the ferrocene moiety attached to the GNC core, which acted as a redox probe. The apparent acid dissociation constant of MUA on the GNC surface estimated from correlation between the amount of adsorbed GNCs and pH of the PAH solutions was in good agreement with those previously reported. Facile charge transport within LBL multilayer assemblies formed under various pH and/or ionic strengths of polymer solution revealed an open porous film microstructure contributing to facile charge transfer by hopping through GNC sites as well as with the aid of electrolyte in pores in such architectures. This study provides significant fundamental basis for construction of highly charged complex structures containing redox groups and useful applications in catalysis and devices fabrication based on charge transfer.