Electrochemical Quantized Capacitance Charging of Surface Ensembles of Gold Nanoparticles

Quantized double layer capacitance charging is observed for monolayers of nanometer-sized monolayer protected gold clusters (Au MPCs) anchored to macroscopic gold electrodes. The clusters were anchored in two ways. One method involves ligand place-exchange binding of an MPC covered with a butanethiolate monolayer to a preformed, self-assembled monolayer of 4,4′-thiobisbenzenethiol (TBBT) on Au. In the second method, an MPC with a mixed TBBT/heptanethiolate monolayer is prepared; this surface-reactive cluster anchors itself onto a gold electrode surface. Differential pulse voltammetry (DPV) of these MPC monolayers displays a succession of current peaks whose regular spacing on the potential axis is similar to that in DPV of solutions of the same, nonanchored MPCs. AC impedance measurements of the MPC monolayers show capacitance undulations that mirror the DPV results.