Significantly Liberating Peroxidase-Mimicking Activity from pH Constraints and Fluorescence Enhancement by Surface Modulation of Copper Nanoclusters: Dual-Modal Sensitive Detection of Antibiotics Kanamycin

Nanozymes have great potential as substitutes for natural enzymes. However, most nanozymes experience unsatisfactory catalytic activity and narrow optimal pH conditions, which greatly limit their wide applications. Herein, we report that copper nanoclusters (Cu NCs) exhibit peroxidase (POD) activity and red fluorescence under optimal pH 3–4 conditions. However, the surface engineering by the Mo(VI) doping and imidazole (IMZ) coordination onto the Cu NCs surface (Mo-IMZ-Cu NCs) can significantly improve the POD-like activity of Cu NCs within a wide pH range (pH 3–9), which broke the pH limitation. In addition, the fluorescence intensity was also greatly enhanced. Mechanism studies suggest that the introduction of Mo(IV) accelerated the electron transfer in the system, which not only greatly boosted the POD activity of Cu NCs but also enhanced the fluorescence of Cu NCs. More interestingly, the POD activity and fluorescence of Mo-IMZ-Cu NCs can be remarkably suppressed by the antibiotic kanamycin (Kana) selectively due to the formation of hydrogen bonding and electrostatic interaction between Kana and Mo-IMZ-Cu NCs, which leads to the aggregation of Mo-IMZ-Cu NCs into a network structure. On the basis of this phenomenon, an enzymatic colorimetry/fluorescence dual-modal platform was explored for the sensitive and selective detection of Kana, with a linear range of 1.5–15,000 nM and a detection limit (LOD) of 0.413 nM (S/N = 3) for the colorimetry mode, and a linear range of 1–10,000 nM and an LOD of 0.174 nM for the fluorimetric assay. Moreover, the as-proposed dual-modal sensor was capable of detecting Kana in real samples. Therefore, this work provides a feasible route to design nanozymes with high activity in a broad pH range, facilitating wide potential applications, including development of bioanalytical techniques.