Tailored Lipid Monolayers Doped with Gold Nanoclusters: Surface Studies and Electrochemistry of Hybrid‐film‐covered Electrodes

Much attention has been given to the electrochemistry and electrochemical applications of Au nanoclusters (AuNCs) because of their unique electrochemical and optical features. However, little is known so far about their assembly with lipids or the formation of biological-nonbiological hybrid monolayers either at the air-water interface or on solid substrates. In this study, we synthesized AuNCs (Au25(SC4)180) with a diameter ca. 0.85±0.25 nm for the gold core, characterized the AuNCs using transmission electron microscopy (TEM) and dynamic light scattering (DLS) and, for the first time, immobilized AuNCs on the electrode in the form of an AuNC-doped lipid monolayer. The Langmuir-Blodgett technique at the air-water interface allowed us to strictly control the composition of the mixed monolayer and monitor changes in the monolayer organization at the air-water interface upon doping with AuNCs. The hybrid monolayer assembly was transferred to an indium-tin oxide (ITO) substrate, and the electrochemical properties of the modified electrode were studied via electrochemical impedance spectroscopy (EIS) and cyclic voltammetry. With an increase in dispersion of the AuNCs in the lipid matrix, the ferrocyanide voltammetry peaks decreased as expected, thereby decreasing the actual conducting area of the electrode. However, the Au nanoclusters also acted as electron transfer mediators in electrode processes proceeding with overpotential, with improved effectiveness shown at very low AuNC concentrations in the lipid layer.