Classified detection of antibiotics using Fe₃O₄@Eu(BDC) as a fluorescent probe

In recent years, fluorescence sensing technology by rare-earth metal-organic frameworks (Ln-MOFs) as probes has garnered extensive attention in the domains of environmental quality testing, pollutant reduction, and biomolecule analysis because of its non-disruptive nature, rapid response, and high sensitivity. The research on aided magnetic controlling has further advanced the industrial value of Ln-MOFs, but the accomplishment of high specificity and rapid recovery still is a challenge for the magnetic Ln-MOFs in practical applications.

A magnetic Ln-MOFs, Fe₃O₄@Eu(BDC), doped with Fe₃O₄ using H₂BDC as the ligand and Eu³⁺ as the central ion through co-precipitation, has been successfully synthesized. It emits red fluorescence when exposed to UV excitation and allows quick separation via magnetic. In sensing assays, Fe₃O₄@Eu(BDC) exhibited fluorescence quenching (FQ) for six classes of antibiotics like nitroimidazole, whereas fluorescence intensity enhancement accompanied by color conversion (FE-CT) were shown for fluoroquinolone antibiotics. The differentiated fluorescence responses are attributed to the internal filtering effect and the energy transfer between the probe and the antibiotic. Fe₃O₄@Eu(BDC) have detection limits as low as 10^-7 M to metronidazole with FQ and levofloxacin with FE-CT in both aqueous and urinary solutions, and can be visually identified by fluorescence intensity or color as an optical signal.

In this paper, a novel synthesis scheme for magnetic Ln-MOFs was proposed, and the prepared Fe₃O₄@Eu(BDC) was applied as a fluorescent probe with high sensitivity for detecting specific antibiotics. According to the variety of antibiotic, the probe can perform different fluorescent responses and then achieved classified detection by naked eyes. Due to ideal magnetic and porous properties, the Fe₃O₄@Eu(BDC) also realized rapid removal and recovery of analytes. This study provided a convenient and efficient strategy for on-site testing and classification of antibiotics, and advanced the practical application of Ln-MOFs.