A Dual‐Mode CA‐125 Immunosensor Based on the Efficient Oxygen Reduction Reaction of Nickel Single‐Atom Catalyst for Promoting the Luminol Electrochemiluminescence

Herein, two carbon‐supported nickel single‐atom catalysts (Ni–N ₂ O ₂ @C, Ni–N ₄ @C) were synthesized and used as efficient coreaction accelerators to enhance the ECL responses of luminol/O ₂ system. The corresponding oxygen reduction reaction (ORR) behaviors of the catalysts can be well controlled by adjusting the coordination environment of the center metal atoms. The catalytic measurements showed that the Ni–N ₂ O ₂ @C catalyst displayed a two‐electron pathway to produce H ₂ O ₂ , while the Ni–N ₄ @C showed a 4e‐ORR route to reduce O ₂ into H ₂ O. According to the experimental results, the O ₂ ^⦁− was the main radical during the ECL reaction process, and the Ni–N ₄ @C catalyst exhibited superior performance in activating the dissolved O ₂ , which is beneficial for enhancing the ECL emission of luminol/O ₂ system. Finally, Ni–N ₄ @C catalyst was used as coreactant promoters in luminol ECL system, and Cu‐based metal–organic framework (Cu‐BTC) was chosen as the masking agent of the electrochemiluminescence (ECL) signal and the signal substance of differential pulse voltammetry (DPV). Based on the abovementioned strategy, a dual‐signal immunosensing platform was constructed, and the sensitive analysis of ovarian cancer biomarker CA‐125 was achieved with high selectivity as well as positive stability.