"Off-on" signal amplification strategy amperometric immunosensor for ultrasensitive detection of tumour marker

Reducing background signal is an effective method to improve the sensitivity of amperometric immunosensors, which are significant in the detection of cancer. Herein, a novel immunosensor probe was synthesised using zeolitic imidazolate framework-hydroquinone-bovine serum albumin (ZIF-8-HQ-BSA). Based on the probe, an "off-on" strategy was applied in the immunosensor to amplify ΔI, the current signal "turn off and on". The ZIF-8-HQ-BSA probe initially showed little current signal since ZIF-8 and BSA exhibit poor conductivity. To amplify the current signal "turn on", the structure of ZIF-8 was broken after treatment with HCl, releasing hydroquinone to be absorbed by the polyaniline hydrogel substrate. Hydroquinone can produce a strong signal and also exhibits strong catalytic ability for H₂O₂ to further enhance the signal. Following this method, the immunosensing platform was used to detect cytokeratins antigen 21-1 (CYFRA21-1) in human serum and revealed a wide liner range from 0.1 pg mL^-1 to 100 ng mL^-1 with a low detection limit of 0.65 pg mL^-1 (S/N = 3), demonstrating good consistency with an electrochemiluminescence immunoassay. Thus, the amperometric immunosensing platform discussed in this work has high potential for application in healthcare monitoring, clinical diagnostics, and biomedical devices.