Cascade-driven dual-signal attenuation antifouling immunosensor for femtogram-level sensing for SCCA.

Nonspecific adsorption compromises the accuracy of electrochemical immunosensors in complex biological samples. Conventional antifouling materials often suffer from poor conductivity, which reduces sensitivity. To address this, a cascade-driven dual-signal attenuation strategy was designed. A hydrophilic conductive composite (GO/AuNPs/PPy/PA/MB, GAPPM) was synthesized via a one‑pot method to fabricate the sensing interface, and capture antibodies were anchored by electrodeposited AuNPs. The immunoprobe was constructed by combining GOx‑encapsulated ZIF‑8 with labeling antibodies linked via in‑situ grown AuNPs. Upon target antigen binding, a sandwich immunocomplex was formed on the electrode surface, and two cascade pathways were activated by glucose: (i) degradation of methylene blue signal molecules was induced, leading to attenuation of the current, and (ii) generation of an insoluble coordination precipitate was promoted, increasing interfacial resistance. Dual‑path cascade signal amplification was thus achieved synergistically. Using squamous cell carcinoma antigen as a model, the immunosensor achieved a detection limit of 29.5 fg mL⁻1 and a wide linear range (1 pg mL⁻1 to 1 µg mL⁻1). Notably, after 30-min incubation in undiluted human serum, the modified electrode exhibited an impedance change 56% lower than that of its BSA‑blocked counterpart, confirming excellent antifouling properties. This strategy holds great promise for high‑performance electrochemical biosensing in complex biological samples.