Ionic Liquid of a Gold Nanocluster: A Versatile Matrix for Electrochemical Biosensors

Ionic liquids are room-temperature molten salts that are increasingly used in electrochemical devices, such as batteries, fuel cells, and sensors, where their intrinsic ionic conductivity is exploited. Here we demonstrate that combining anionic, redox-active Au-25 clusters with imidazolium cations leads to a stable ionic liquid possessing both ionic and electronic conductivity. The Au-25 ionic liquid was found to act as a versatile matrix for amperometric enzyme biosensors toward the detection of glucose. Enzyme electrodes prepared by incorporating glucose oxidase in the Au-25 ionic liquid show high electrocatalytic activity and substrate affinity. Au-25 clusters in the electrode were found to act as effective redox mediators as well as electronic conductors determining the detection sensitivity. With the unique electrochemical properties and almost unlimited structural tunability, the ionic liquids of quantum-sized gold clusters may serve as versatile matrices for a variety of electrochemical biosensors.