A single-atom Cu-N 2 catalyst eliminates oxygen interference for electrochemical sensing of hydrogen peroxide in a living animal brain.

Hydrogen peroxide (H 2 O 2 ) plays essential roles in various physiological and pathological processes. The electrochemical hydrogen peroxide reduction reaction (HPRR) has been recognized as an efficient approach to H 2 O 2 sensing; however, the HPRR has always suffered from low tolerance against the oxygen reduction reaction (ORR), resulting in poor selectivity of the HPRR-based sensing platform. In this study, we find that the electrochemical HPRR occurs preferentially compared to the ORR when isolated Cu atoms anchored on carbon nitride (Cu 1 /C 3 N 4 ) are used as a single-atom electrocatalyst, which is theoretically attributed to the lower energy barrier of the HPRR than that of the ORR on a Cu 1 /C 3 N 4 single-atom catalyst (SAC). With the Cu 1 /C 3 N 4 SAC as the electrocatalyst, we fabricated microsensors that have a good response to H 2 O 2 , but not to O 2 or other electroactive neurochemicals. When implanted into a living rat brain, the microsensor shows excellent in vivo sensing performance, enabling its application in real-time quantitative investigation of the dynamics of H 2 O 2 production induced by mercaptosuccinate and glutathione monoethyl ester in a living animal brain.