Conformational fixation induced fluorescence turn-on of oxytetracycline coordinated on aluminum-based metal-organic frameworks for ultrasensitive sensing application

Since the abuse of oxytetracycline (OTC) has brought serious environmental problems, it is of great practical significance to develop sensitive OTC fluorescent probes to quantify environmental OTC residues. Herein, the aluminum-based metal-organic framework MIL-53(Al) with microflower morphology and plentiful surface open aluminum sites (denoted as FMIL-53(Al)) was tailored via an acetic acid-assisted solvothermal method and subsequently exploited for ultrasensitive detection of OTC. Compared with conventional hydrothermally synthesized MIL-53(Al), FMIL-53(Al) possesses a larger specific surface with plentiful open aluminum sites, which can selectively coordinate with OTC to fix the molecular conformation. The coordinated OTC molecules undergo a transition from twisted-conformation to extended-conformation, accompanied by an increase in fluorescence quantum yield. As a fluorescent probe, the detection limit of FMIL-53(Al) for OTC is estimated as low as 0.94 nM. Finally, the FMIL-53(Al)-based probe can be applied for the detection of OTC in water samples of fish farm pond, and a portable test paper was successfully fabricated for on-site visual identification of OTC. This work not only demonstrates a novel morphology of MIL-53(Al) for OTC ultrasensitive sensing but also provides an example of morphological engineering to optimize the performance of MOF-based fluorescence sensors.