Gold Nanocluster-Promoted Interfacial Electron Transfer of Cytochrome c at an Aqueous–Organic Interface

Functional enzyme-gold nanoparticle bioconjugates are becoming increasingly important in bioelectrocatalysis since they facilitate and improve the efficiency of long-range protein interfacial electron transfer between enzymes and electrodes by enhancing conductivity. While much research has focused on solid-liquid interfaces, there is still limited understanding of the key parameters and electrochemical conditions necessary for reliable and reproducible bioelectrochemistry at polarizable aqueous-organic interfaces under native conditions. Herein, we demonstrate how the size of gold-modified nanoparticles influences the interfacial electron transfer of cytochrome c at an aqueous-organic interface. We found that nanoclusters centered in a size of 1.2 nm, equivalent to the water-trifluorotoluene mixed solvent layer (ca. 1.5 nm), work in tandem with cytochrome c to facilitate oxygen reduction reactions. In contrast, bioconjugates comprising larger gold nanoparticles are less effective in enhancing cytochrome c electrochemistry, with the gold nanoparticles acting as independent catalysts at the interface.