POM-mediated MOFs-based probes facilitate multistep cascade reaction for ultrasensitive detection of tumor marker

Metal-organic frameworks (MOFs) are often used as carriers for catalytically active substances and play the role of signal amplifiers in electrochemical immunosensors. However, catalytically active species often form aggregates in MOFs, resulting in negative effects such as reduced specific surface area and reduced catalytic activity. Here, we use the spatial confinement of zeolitic imidazolate framework-8 (ZIF-8) to anchor polyoxometalate (POM), and cooperate with xanthine oxidase (XOD) to achieve multistep cascade amplification of electrochemical signals. In the presence of the substrate hypoxanthine, XOD catalyzes the production of H2O2, which is mediated by POM to amplify the electrochemical signal of thionine. The proposed immunosensor of cytokeratin 19 fragments 21–1 exhibited a wide detection range (100 fg mL-1 to 1 μg mL-1) and an ultralow detection limit of 44.92 fg mL-1. Our work provides the pathway for the gentle preparation of probes with high catalytic site dispersion.