Multi-metal MOF-on-MOF metal-organic gel-based visual sensing platform for ultrasensitive detection of chlortetracycline and D-penicillamine.

The widespread presence of antibiotic residues in the environment and food represents a significant threat to human health. In this study, a novel MOF-on-MOF (FCZE) gel with excellent peroxidase activity and strong fluorescence properties successfully synthesized by using Polyvinyl pyrrolidone (PVP) as a cross-linker and H₄BTEC as a ligand. Based on the energy transfer from the FCZE ligand to Eu luminescence, an ultrasensitive fluorescence method was developed for the detection of chlortetracycline (CTC), achieving a limit of detection (LOD) as low as 0.43 nM. Furthermore, the combination of FCZE with the 3,3',5,5'-tetramethylbenzidine (TMB)-hydrogen peroxide (HO) system enabled sensitive colorimetric detection of D-penicillamine (D-PA) with an LOD of 8.66 nM. Theoretical calculations reveal that the fluorescence quenching of FCZE by CTC is attributed to the inner filter effect of CTC and its suppression of the HBTEC excited-state return to the ground state. Furthermore, Fukui function was employed for the first time to clarify the role of D-PA in scavenging free radicals and reducing oxidized TMB (oxTMB), providing a comprehensive understanding of the colorimetric detection mechanism. Additionally, a smartphone-assisted visual detection platform based on FCZE was developed for the detection of CTC and D-PA, with LODs of 0.71 μM and 0.13 μM, respectively. This study highlights the potential of nanomaterials for the simultaneous detection of multiple antibiotics, offering a novel strategy for the rapid and efficient monitoring of antibiotic residues in environmental samples.