Self-assembling of monolayer-protected gold nanoparticles

Self-assembling of monolayer-protected gold nanoclusters onto a gold electrode surface was reported. The particles were surface-active with multiple copies of peripheral thiol groups that resulted from an exchange reaction with alkanedithiols. Excessive dithiol and displaced thiol ligands were removed from the cluster exchange solution via liquid extraction using a hexane-methanol system. The self-assembling process appeared to be rather fast, similar to that for simple alkanethiols. The resulting particle adlayers exhibited discrete electron-transfer features that were ascribed to the quantized capacitance charging to the particle double layers. The electrode double-layer capacitance, evaluated from impedance measurements, also showed a modulation with electrode potentials. Consistent electron-transfer rate constants were obtained from the Laviron evaluation as well as from the impedance measurements. The electron-charging behaviors were also quite visible in aqueous media when the interparticle "void" space was filled up with low-dielectric organic adlayers. Technical implications of these particle assemblies were also discussed.