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 Cu 2 O 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.

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A novel signal on−off glutathione (GSH) electrochemical sensor was developed based on a AuCu bimetaldecorated Zr-containing metal−organic framework (Zr-MOF), in which a signal amplification strategy promoted by solid-state electrochemistry of cuprous chloride (CuCl) was used. The Zr-MOF with a large surface area can be effectively used as the substrate for the in situ growth of AuCu bimetals to obtain the Zr-MOF@AuCu nanocomposite. The interaction between Cu in Zr-MOF@AuCu and Cl − in the solution accompanied with the formation of CuCl displays an enlarged stable oxidation current, which greatly declines with the addition of GSH owing to the specific Cu−GSH interaction. The conversion of CuCl into Cu-GSH triggered the "crowding-out effect" and resulted in a sharp drop in the peak current of CuCl, which can realize the ultrasensitive and selective detection of GSH. The detection mechanism was investigated, and the detection range was 10 pM−1 mM with the detection limit as low as 2.67 pM. The special response mechanism for the detection of GSH allows the highly selective detection of GSH in various real samples with reliable results, endowing the proposed electroanalysis sensor with broad application prospects in biological and food analysis.

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