Ultrasensitive Cr(VI) sensing via H2O2-free electron-accepting pathway using atomically dispersed CuCo-NC.

Hexavalent chromium (Cr(VI)), a highly toxic and carcinogenic environmental pollutant, poses severe threats to ecological balance and human health. Traditional colorimetric detection methods relying on peroxidase-like nanozymes often suffer from interference caused by reactive oxygen species (ROS) and coexisting redox-active substances, compromising their accuracy in complex water matrices. Herein, we report a novel H2O2-free colorimetric strategy for the ultrasensitive detection of Cr(VI) using atomically dispersed CuCo-NC catalysts. Unlike conventional mechanisms, the synergistic interplay between Cu and Co atoms modulates the electronic structure (d-band center), enabling Cr(VI) to act as a direct electron acceptor. This unique pathway facilitates the oxidation of TMB without generating ROS intermediates, thereby conferring exceptional resistance to common interferents such as Fe2+/Fe3+. The sensor exhibits a wide linear range (50-1000 nM) and an ultralow detection limit of 1.12 nM, surpassing many existing methods. Furthermore, the practical applicability of this probe is validated through the successful monitoring of Cr(VI) in real water samples (e.g., Guilin Lijiang River), demonstrating its robustness for on-site environmental surveillance. This work not only provides a reliable tool for early-warning monitoring of chromium pollution but also offers mechanistic insights into H2O2-free catalytic pathways.