Direct Electron Transfer to a Metalloenzyme Redox Center Coordinated to a Monolayer-Protected Cluster

A strategy for establishing electrical contact to the metal center of a redox metalloenzyme, galactose oxidase (GOase), by coordination of a linker attached to a monolayer-protected gold cluster is presented. The cluster-enzyme hybrid system was first prepared in solution and characterized by high-angle annular dark-field scanning transmission electron microscopy. Electrochemical communication between a gold electrode and GOase was achieved by first modifying the electrode surface with a biphenyl dithiol self-assembled monolayer followed by reaction with gold clusters capped with thioctic acid. GOase was then immobilized by replacement of the H2O Molecule at the Cull exogenous site by coordination of a carboxylate-terminated gold cluster. This chemical attachment ensured electrical contact between the redox center and the electrode, leading to direct mediatorless electron transfer to the protein. Hybrid systems can find applications in biosensors and biofuel cells and for studying electrochemically the catalytic mechanism of reactions for which free radicals and electron-transfer reactions are involved. The present results can be extended to other metalloenzymes.