A ROS-competitive dual-potential ratiometric ECL immunosensor for ultrasensitive CA15-3 detection based on...

Conventional luminol-based electrochemiluminescence (ECL) systems are constrained by low luminescence efficiency and stability, largely due to unstable hydrogen peroxide and inefficient dissolved oxygen conversion to reactive oxygen species (ROS). Here, the oxygen evolution reaction (OER) is harnessed to supply abundant ROS, which not only enhances the anodic ECL of luminol but also enables stable cathodic emission from CdSe quantum dots (QDs). To address these issues and circumvent false positive/negative signals common in ECL assays, a novel dual-potential ratiometric ECL sensor based on a competitive ROS mechanism was developed for the ultrasensitive detection of carbohydrate antigen 15-3 (CA15-3). A boron-doped and selenium vacancy-modified nickel selenide/poly(5-aminoindole) (B_x-NiSe/P5AIn) nanocomposite was first synthesized, which synergistically boosts OER catalytic activity through non-metal doping and defect engineering, thereby significantly amplifying the anodic ECL signal of luminol via ROS generation. Upon recognition of the target antigen, CdSe QDs labeled on the secondary antibody competitively consume ROS, leading to the enhancement of cathodic ECL and the attenuation of the anodic signal, thus establishing a ratiometric response model. The sensor exhibits a wide linear range from 0.001 to 100 U mL^-1 for CA15-3 with a detection limit as low as 0.0003 U mL^-1, demonstrating substantially improved sensitivity over conventional methods. This work not only provides an effective tool for early screening and diagnosis of breast cancer, but also opens a new avenue for designing multi-signal ECL sensing systems through catalysis-competition regulatory mechanisms.