Eu3+-functionalized metal-organic framework composite as ratiometric fluorescent sensor for highly selective detecting urinary 1-hydroxypyrene

An anionic three-dimensional metal-organic framework of JXNU-4 with one-dimensional channels occupied by the extraframework dimethylammonium cations was chosen as a parent compound to host Eu3+ cations by uncoordinated carboxylate oxygen atoms in its pores through a cation exchange experiment. The Eu3+-incorporated sample Eu3+@JXNU-4 is structurally characterized and displays excellent Eu3+ luminescence and good fluorescence stability in aqueous solution, which is resulted from the sensitization and protection provided by the parented framework. The Eu3+@JXNU-4 was developed as a fluorescent probe for urine 1-hydroxypyrene (1-HP), which is a biomarker of polycyclic aromatic hydrocarbons (PAHs) carcinogens and represents the internal dose of PAHs exposure in the human body. In the presence of 1-HP, the 1-HP emission emerges and Eu3+@JXNU-4 exhibits 1-HP- and Eu3+-based dual emission. The intensity of the 1-HP emission increases with the concentration of 1-HP increasing, while the Eu3+ emission recedes in the meantime. The ratio value of 1-HP emission at 502 nm (1502) and Eu3+ emission at 616 nm (1616) versus the concentration of 1-HP reveals a good linear relationship, which indicates the Eu3+@JXNU-4 is an excellent candidate for ratiometric fluorescence sensing for 1-HP. Finally, the fluorescence mechanism was discussed.