Copper peroxide/ZIF-8 self-producing H₂O₂ triggered cascade reaction for amperometric immunoassay of carbohydrate antigen 19-9

Generally, H₂O₂ is frequently adopted to improve analysis capabilities of various detection systems. However, the addition of H₂O₂ with relatively higher concentration can lower the bioactivity of antibodies or antigens and the sensing interface stability in most peroxidase and peroxidase-like immunosensors. In order to solve these issues, we designed a novel copper peroxide/ZIF-8 immunoprobe that can self-produce H₂O₂ to trigger a cascade reaction for the sensitive detection of carbohydrate antigen 19-9. Specifically, CP/ZIF-8 plays a key role as a "signal switch" in the immunosensor. In the presence of HCl, the structures of ZIF-8 and copper peroxide can be broken, producing Cu²⁺ and H₂O₂ and a subsequent Fenton-type reaction that generates •OH. The resulting •OH can induce the decomposition of 3-aminobenzeneboronic acid/poly (vinyl alcohol) (PVA) film on the electrode. Although the immunosensor initially showed little current signal due to the poor conductivity pf ZIF-8 and PVA, the current signal was significantly amplified by a HCl-triggered cascade reaction. Under optimal conditions, the immunosensor displayed a wide linear range from 0.0001 to 100 U mL^-1 with an ultralow limit of detection of 53.5 μU mL^-1 (S/N = 3) for carbohydrate antigen 19-9. Considering these advantages, namely self-producing H₂O₂ and easy operation, this strategy paves a new way to design other novel sensors.