Ionic ligand mediated electrochemical charging of gold nanoparticle assemblies.

We demonstrate that ionic surface functionalization is well-suited for controlling the electrochemical charging of nanoparticle assemblies. Gold nanoparticles approximately 2 nm in diameter were functionalized with between 0 and approximately 3.3 cationic thiols per particle and the coupled motion of ions and electrons during redox cycling (charging) was followed in situ using an electrochemical quartz-crystal microbalance. When the electrochemistry is performed using a polycation electrolyte too large to penetrate the nanoparticle film, the degree of reduction possible was found to be dictated by the number of cationic ligands on the particle surface available for charge compensation. This route to reduced particles might be useful for electronic device fabrication, since the negative electronic charge is precisely compensated by immobile cationic ligands.