Single-Electron Charging of Thioctic Acid Monolayer-Protected Gold Clusters

There is great interest in the use of Monolayer-Protected Gold Clusters (AuMPCs) as nanoscale capacitors in aqueous media for nanobiotechnological applications, such as bioelectrocatalysts, biofuel cells, and biosensors. However, AuMPCs exhibiting subattofarad double-layer capacitance at room temperature, and the resolution of single-electron charging, has been mainly obtained in an organic medium with nonfunctional capping ligands. We report here the synthesis of Thioctic Acid Monolayer-Protected Au Clusters (TA-AuMPCs) showing electrochemical single electron quantized capacitance charging in organic and aqueous solutions and when immobilized onto different self-assembled monolayer-modified gold electrodes. The presence of functional carboxylic groups opens a simple strategy for interfacing a nanoparticle assembly to biomolecules for their use as electron donors or acceptors in biological electron transfer reactions.