Gold nanoparticle assemblies by metal ion-pyridine complexation and their rectified quantized charging in aqueous solutions

Gold nanoparticle assemblies were constructed by exploiting the complexation interactions between divalent metal ions and pyridine moieties. The thickness (layers) of the particle thin films was readily controlled by the repetition of the alternate dipping cycles, as monitored by quartz crystal microbalance (QCM). Electrochemical studies of these surface-immobilized nanoparticle layers revealed rectified quantized charging characters in aqueous solutions in the presence of hydrophobic anions. The effects of the nature of the electrolyte ions were investigated in the context of their hydrophobicity and interactions with the surface-bound particle molecules. It was found that the onset voltammetric potentials, as well as the effective molecular capacitance of the nanoparticles, were sensitive to the solution compositions. The behaviors were quite similar to those with the nanoparticle assemblies fabricated by dithiol linkages. The present study provided additional experimental parameters that could be used for the manipulation of nanoscale electron transfer.