A luminescent MOF as a fluorescent sensor for the sequential detection of Al3+ and phenylpyruvic acid

Aluminum is a widely distributed element with potential harm to human health, and the analysis of phenylpyruvic acid (PPA) is also routine in clinical uroscopy for metabolic disorders. In this work, we synthesized a UiO-66-backboned MOF, UiO-66-(OH)2, to construct an “off–on–off” platform for the sequential fluorescence detection of Al3+ and PPA. With incorporated hydroxyl groups, this MOF could capture Al3+ ions in aqueous solution and show enhanced fluorescence response through an excited-state intramolecular proton transfer mechanism. The binding affinity of PPA to Al3+ is stronger than that to the MOF; therefore, the further addition of this compound to UiO-66-(OH)2–Al3+ extracts the adsorbed Al3+ and restores the original weak emission of the MOF. UiO-66-(OH)2 exhibited good selectivity and sensitivity (DL = 47 nM for Al3+ and 100 nM for PPA) in both steps of detection and was successfully applied to the analysis of PPA in artificial urine.