A nitrogen-rich Eu-MOF for ultrasensitive fluorescence detection of 6-mercaptopurine and 6-thioguanine.

The simultaneous detection of toxic antineoplastic drugs 6-mercaptopurine (6-MP) and 6-thioguanine (6-TG) remains challenging due to their low intrinsic luminescence and low quantum yield. To address this, a novel three-dimensional europium-based metal-organic framework, Eu2-tbia, was rationally constructed using a triazole-dicarboxylate ligand, 5-((4'-(triazol-1-yl)benzyl)oxy)isophthalic acid (Htbia). The obtained Eu2-tbia exhibits strong luminescence via an efficient antenna effect and retains excellent stability in aqueous solutions over a wide pH range and in various organic solvents. The framework features abundant uncoordinated nitrogen sites that enable specific recognition of 6-MP and 6-TG, leading to rapid fluorescence quenching and achieving ultralow detection limits of 84 nM and 142 nM, respectively. Additionally, Eu2-tbia demonstrates outstanding selectivity and anti-interference capability in complex matrices. Density functional theory calculations further investigated the synergistic effect between the inner filter effect and host-guest interactions underlying the detection mechanism, as well as the electron transfer behavior of Eu2-tbia during the fluorescent sensing process. This work not only establishes Eu2-tbia as a robust sensing platform for monitoring purine analogs in biomedical and environmental applications but also provides fundamental insights into the structure-property relationships of MOF-based sensors.