Numerous strategies have been developed to improve the intensity of a luminol electrochemiluminescence (ECL) system due to the low quantum yield of luminol. Notably, considerable research was carried out to improve luminol ECL intensity relying on increasing the concentration of reactive oxygen species (ROS). Herein, a Co–N x –C electrocatalyst treated with nitric acid or hydrochloric acid (named as Co-POC-O or Co-POC-R, respectively) was in situ prepared on the surface of carbon nanotubes. Surprisingly, compared with Co-POC-R, the Co-POC-O electrocatalyst not only displays excellent oxygen reduction reaction (ORR) performance but also enriches luminol via non-covalent bonds rather than covalent bonds and physical mixing. This method improves the amount of luminol involved in the electrochemical reaction as well as shortens the distance for electron transfer between oxidized luminol and ROS, which significantly enhances the ECL intensity (10-fold higher than that of the bare electrode and 2-fold higher than that of Co-POC-R). The platform realizes highly sensitive dopamine (DA) with a detection limit of 1.0 pM and a linear range from 10 pM to 1.0 nM. In this work, Co-POC-O is both the co-reaction accelerator and carrier material of luminophore species, which provides a new idea to realize ECL signal amplification.

The lumiol-O2 electrochemiluminescence (ECL) system constantly emits bright light at positive potential. Notably, compared with the anodic ECL signal of the luminol-O2 system, the great virtues of cathodic ECL are that it is simple and causes minor damage to biological samples. Unfortunately, little emphasis has been paid to cathodic ECL, owing to the low reaction efficacy between luminol and reactive oxygen species. The state-of-the-art work mainly focuses on improving the catalytic activity of the oxygen reduction reaction, which remains a significant challenge. In this work, a synergistic signal amplification pathway is established for luminol cathodic ECL. The synergistic effect is based on the decomposition of H2O2 by catalase-like (CAT-like) CoO nanorods (CoO NRs) and regeneration of H2O2 by a carbonate/bicarbonate buffer. Compared with Fe2O3 nanorod (Fe2O3 NR)- and NiO microsphere-modified glassy carbon electrodes (GCEs), the ECL intensity of the luminol-O2 system is nearly 50 times stronger when the potential ranged from 0 to −0.4 V on the CoO NR-modified GCE in a carbonate buffer solution. The CAT-like CoO NRs decompose the electroreduction product H2O2 into OH· and O2 · –, which further oxidize HCO3 – and CO3 2– to HCO3 · and CO3 · –. These radicals very effectively interact with luminol to form the luminol radical. More importantly, H2O2 can be regenerated when HCO3 · dimerizes to produce (CO2)2*, which provides a cyclic amplification of the cathodic ECL signal during the dimerization of HCO3 ·. This work inspires developing a new avenue to improve cathodic ECL and deeply understand the mechanism of a luminol cathodic ECL reaction.