A defective Fe–N ₃ –C single-atom nanozyme for the detection of carcinoembryonic antigen

Carcinoembryonic antigen (CEA), a pan-cancer biomarker, holds critical clinical value in aiding diagnosis and prognostic assessment of various malignancies. The development of a facile, accurate, and selective CEA detection method remains an urgent need. Herein, we developed a facile colorimetric sandwich immunoassay based on a highly defective Fe-based single-atom nanozyme (dFeSA) for detecting CEA. The dFeSA with an Fe-N₃-C active site exhibited remarkable oxidase-like activity, enabling the catalytic conversion of O₂ to superoxide radicals and subsequent oxidation of chromogenic substrates. This method achieved high sensitivity and specificity for CEA detection over a wide range (0.05-300 ng mL^-1) and a low detection limit of 0.017 ng mL^-1. Notably, the immunoassay demonstrated exceptional performance for CEA detection in real serum samples with recovery rates of 92.7%-102.6%. This colorimetric immunoassay represents a robust analytical platform for CEA detection, offering a cost-effective alternative to conventional methods and holding significant potential for early cancer diagnosis and prognostic monitoring in clinical practice.