Au/Metal–Organic Framework Nanocapsules for Electrochemical Determination of Glutathione

An ultrasensitive signal amplification strategy has been developed using Au@Cu-MOF nanocapsules as an electrochemical platform for the determination of glutathione (GSH) based on the signal output from solid-state electrochemistry of cuprous chloride (CuCl). The Au@Cu-MOF nanocapsule, with a metal–organic framework (MOF) sandwich shell and an encapsulated Au nanoparticle layer, was prepared via coordinate replication of a Cu2O redox-template strategy. Also, the Au@Cu-MOF nanocapsule-modified electrode achieved boosting signal output in the presence of chlorine ions (Cl–) by solid-state electrochemistry of CuCl, which showed a pair of remarkable peaks. However, in the presence of GSH, the phenomenon termed as "crowding-out effect" appeared, in which the specific Cu–GSH interaction triggered the competitive reaction with the conversion of CuCl into nonelectroactive substance of Cu–GSH, leading to a sharp decrease in the peak current of CuCl. The Au@Cu-MOF nanocapsule-modified electrode showed high sensitivity toward GSH owing to the specific electrochemical output at a relatively low potential, which can effectively shield the possible interferences from complex physiological surroundings. The crowding-out effect can also improve the selectivity, particularly for complex analytical samples in terms of electrode fouling. The electrochemical sensor showed a wide linear range of 0.01–40 nM and 40 nM to 10 μM, with a detection limit of 2.5 pM (S/N = 3). The sensor can be utilized for the determination of GSH in various real vegetable and serum samples with satisfactory results. Besides, it can also be applied for probing GSH in the lysates of Romas cells with good sensitivity, which brings dawn for early diagnosis of cancer in clinics. Moreover, the ultrasensitive and selective solid-state CuCl electrochemistry-promoted signal amplification strategy as well as the excellent stability and special nature of Au@Cu-MOF nanocapsules may promise their wide application in biological and food analysis fields.