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 H 2 O 2 -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 Fe 2+ /Fe 3+ . 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 H 2 O 2 -free catalytic pathways. Graphical abstract Schematic illustration of the H 2 O 2 -free colorimetric sensing strategy using atomically dispersed CuCo-NC nanozymes. The synergistic Cu/Co dual sites enable Cr(VI) to act as a direct electron acceptor, bypassing the generation of reactive oxygen species (ROS) and thus eliminating interference from coexisting redox-active substances. This mechanism allows for the ultrasensitive and selective visual detection of Cr(VI) in real water environments