ZIF-8 silencing shell removed by complexation competition reaction for ultrasensitive electrochemical immunoassay

Aiming to develop a stable and simple immunosensor with superior performance, we designed a new strategy based on complexation competition reaction among CaCO3, zeolitic imidazolate framework (ZIF)-8 and ethylenediamine tetraacetic acid disodium (EDTA) for electrochemical detection of cytokeratin 19 fragment 21-1 (CYFRA21-1). First, immunocomplex was formed by CaCO3-Au modified with antibody, MBs modified with antibody and antigen in tube. Then, excess EDTA was added for complexation reaction with CaCO3 and supernatant containing EDTA without complexation reaction was obtained. Second, Ag nanoparticles (NPs) as signal substance were electrodeposited on the electrode surface, and silenced by ZIF-8 layer generated in situ. The remained EDTA in supernatant was transferred to electrode for etching ZIF-8. The signal of Ag NPs was reactivated, owning to partly removing silencing layer of ZIF-8. Therefore, the concentration of target analyte was quantitatively detected by measuring the current signal of Ag/AgCl. Under optimal conditions, the electrochemical immunosensor had an ultralow detection limit of 3.175 fg mL(-1) for CYFRA21-1, with a wide detection range from 10 fg mL(-1) to 1 mu g mL(-1). This work successfully constructed an immunosensor based on complexation competition reaction, which providing a potential route for clinical analysis.