Single-Atom Iron Boosts Counter Electrode Electrochemiluminescence for Biosensing

Traditional electrochemiluminescence (ECL) detection makes it difficult to realize the spatial separation of the sensing and reporting sides, which inevitably causes mutual interference between the target and the luminescent substance. By studying the relationship between the luminol luminescence position and electrode potential in a three-electrode system, this work realized spatial separation of the sensing and reporting sides for the first time. Experimental investigations showed that luminol only emitted ECL signals at electrodes with positive polarity, regardless of whether a positive or negative voltage was applied. Inspired by this, we introduced a carbon vacancy-modified iron single-atom catalyst (V_C-Fe-N-C SAC) with excellent oxygen reduction reaction (ORR) activity into the working electrode, which can catalyze the reduction of dissolved O₂ to produce abundant reactive oxygen species (ROS). ROS diffused to the surface of the counter electrode to oxidize luminol and produce a high-intensity ECL signal at an ultralow trigger potential. As a proof-of-concept application, a sensitive ECL biosensor with spatial separation of the sensing and reporting sides was first constructed for microcystin-LR (MC-LR) detection. This work solved the interference between the target and luminescent substance in the traditional three-electrode ECL system and improved the detection accuracy and sensitivity. Furthermore, the introduction of single-atom catalysts (SAC) avoided the use of the coreactant H₂O₂ and the tedious electrochemical oxidation process of luminol, which broadened the application of ECL biosensors.