A valence-state-defect–mediated copper nanocluster nanozyme with high peroxidase-like activity for multimodal colorimetric detection of mercury( <scp>ii</scp> )

Nanozyme-based colorimetric analysis has potential applications in environmental monitoring and food safety. Here, we report a novel copper nanocluster (CuNC) nanozyme with high peroxidase-like activity. The results demonstrate exceptional catalytic activity of up to 114.29 U mg^-1 in the presence of high oxidation state Cu²⁺ species. Accordingly, a CuNC-based colorimetric platform was established for high selectivity Hg²⁺ monitoring with a limit of detection of 4.21 nM. Excitingly, the color change induced by Hg²⁺ can be detected not only with the naked eye but also using a smartphone, without the need for sophisticated instruments or trained personnel. This work not only provides an economical and reliable multimodal detection method for Hg²⁺ but also enriches the existing armory of nanozymes in colorimetric studies and beyond.