Intelligent hydrogel and smartphone-assisted colorimetric sensor based on Bi-metallic organic frameworks for...

A smartphone-integrated colorimetric sensor is introduced for the rapid and simultaneous detection of kanamycin (KAN) and oxytetracycline (OTC). This sensor relies on the peroxidase-mimicking activity of Fe/Zr Bi-metallic organic frameworks (UIO-66(Fe/Zr)-NH₂). This Bi-metallic MOF can facilitate the oxidation of a colorless substrate, 3,3',5,5'-tetramethylbenzidine (TMB), by reactive oxygen species (ROS) derived from hydrogen peroxide (H₂O₂), resulting in the formation of blue-colored oxidized TMB (ox-TMB). Consequently, Fe/Zr MOF was utilized for the detection of KAN and OTC under optimized conditions. In the presence of KAN and OTC, the interaction between TMB and H₂O₂ is inhibited, resulting in varying colorimetric responses. The approach accurately measured KAN and OTC, with detection limits as low as 0.44 and 6.86 nM, respectively. To achieve real-time and portable analysis even in harsh conditions, the proposed sensor was integrated with hydrogel-assisted smartphone technology thereby eliminating the need for expensive and cumbersome laboratory-based testing apparatus. Furthermore, the sensor was successfully used for real water sample analysis, with good recovery results. The proposed sensor provides a quick, visual, and highly sensitive approach for the simultaneous and accurate determination of KAN and OTC residues in polluted water, even at trace quantities. This study advances the application of MOF-based nanozymes in environmental monitoring, while also offering extensive opportunities for use in other fields.