Biphasic zinc-based metal-organic frameworks composite for ultrasensitive fluorescent detection of oxytetracycline

Two zinc-based metal-organic frameworks were synthesized via a solvothermal method using ascorbic acid and 1,3,5-benzenetricarboxylic acid. X-ray diffraction analysis revealed that the ascorbic acid composite exhibits two crystalline phases, whereas the other composite exhibits a single monoclinic phase. TEM analysis shows homogeneous nanoparticles ranging from 10 to 90 nm. The biphasic composite emits red-orange fluorescence at 612 nm, with quenching dependent on the concentration of oxytetracycline, reaching a detection limit of 1.86 nM under optimized conditions. It demonstrates exceptional selectivity toward oxytetracycline, with a selectivity factor of 39.3. No interference effect was noted with amino acids or milk ions. The method was successfully applied to tap water and milk samples, with recoveries ranging from 98.34% to 110.13% and standard deviations below 6.27%. The time-dependent density functional theory indicates that fluorescence quenching can be attributed to photoinduced electron transfer (PET), making the composite a highly sensitive and selective fluorescent platform.