Synergistic peroxidase-like activity of the Cu-Zn MOF-incorporated g-C3N4 nanozyme integrated with a smartphone-based colorimetric sensor for ciprofloxacin detection.

Antibiotic contamination in water has emerged as a serious global threat to environmental safety and human health. Nanozyme-based optical sensors have demonstrated significant potential for the rapid and highly sensitive detection of antibiotics in environmental samples. Therefore, herein, we have developed a new synergistic hybrid nanozyme (Cu-Zn-MOF/g-C3N4) based on Cu-Zn-MOF-incorporated g-C3N4 nanosheets. This hybrid nanozyme enables the oxidation of TMB through OH radical generation via a Fenton-like reaction involving Cu2+/Cu+ on the nanozyme surface, while the framework stability is achieved through stabilization by Zn2+, and the conjugated g-C3N4 enhances electron transfer for the generation of reactive oxygen species. Importantly, the peroxidase-like activity of Cu-Zn-MOF/g-C3N4 was selectively and significantly enhanced in the presence of ciprofloxacin (CIP) owing to a specific interaction between the nanozyme and CIP. This interaction further accelerates electron transfer, thereby promoting efficient oxidation of TMB. Furthermore, the proposed colorimetric CIP sensor exhibits a rapid response toward CIP and a broad linear range of 2-200 µM with a low detection limit of 0.66 µM. To meet the requirements for on-site colorimetric detection, the system was integrated with a portable smartphone-assisted RGB platform, enabling the in situ determination of CIP in environmental water samples. These findings highlight the critical role of bimetallic coordination in modulating the electronic properties of hybrid nanomaterials, thereby establishing this system as a promising platform for rapid, cost-effective, and sensitive visual detection in environmental monitoring applications.