Single-atom iron boosts electrochemiluminescence for ultrasensitive carcinoembryonic antigen detection

A simple and ultrasensitive sandwich-type electrochemiluminescence (ECL) immunosensor has been developed using porous three-dimensional gold nanoparticles (Au NPs) iron(Fe)–zinc(Zn) metal–organic frameworks (Au NPs–FeZn–MOFs@luminol) as high-efficiency ECL signal probes with Fe single-atom catalysts (SACs) (Fe–N–C SACs) as potentially advanced coreaction accelerators and dissolved oxygen as a coreaction agent to realize an H₂O₂-free amplification method for detecting carcinoembryonic antigen (CEA). The cathodic ECL of luminol, which was usually negligible, increased first. Because the Fe–N–C SACs exhibited an outstanding catalytic performance and a unique electronic structure, different reactive oxygen species (ROS) were generated via the oxygen reduction reaction. ROS oxidized the luminol anions to luminol anion radicals, preventing the time-consuming luminol electrochemical oxidation. Furthermore, the luminol anion radicals generated in situ reacted with ROS to produce potent cathodic ECL emissions. The immunosensor exhibited favorable analytical accuracy (detection range: 0.1 pg mL⁻¹ – 80 ng mL⁻¹), and its detection limit for serum samples was 0.031 pg mL⁻¹ (S/N = 3). Consequently, the proposed strategy offers a new approach for early screening of CEA.