Universal MOF nanozyme-induced catalytic amplification strategy for label-free electrochemical immunoassay

Label-free immunoassay is confronted with a great challenge that its insufficient sensitivity for low concentration analytes, which can be assigned to the low catalytic efficiency of modified materials towards electroactive molecules. Herein, a universal MOF nanozyme-induced catalytic amplification strategy was proposed for constructing highly sensitive label-free electrochemical immunoassay. Specifically, the synthesized CuFe-MOF nanozyme with superior peroxidase (POD)-like activity, regarding as a MOF nanozyme model, can catalyze hydrogen peroxide to produce hydroxyl radicals (•OH), which can efficiently oxidize electroactive probe (such as 1,2-phenylenediamine (o-PD)) accompanying with intense electrochemical signals. Modification of MOF nanozyme on the electrode and capture of antibodies for binding target antigens hinder the catalytic process of MOF nanozyme toward o-PD, resulting in a gradual decrease in electrochemical signal with increasing target antigen concentration, enabling quantitative label-free immunoassay. Thus, a highly sensitive label-free immunosensor using MOF nanozyme-induced catalytic amplification achieved effective detection of Immunoglobulin G (IgG) with a wide linear range of 0.001-50 ng/mL and low detection limit of 0.45 pg/mL. This work proposes a promising nanozyme-induced catalytic amplification strategy for the development of label-free electrochemical immunoassay.