On-Off Ratiometric Fluorescence Europium(III) Metal-Organic Framework for Quantitative Detection of the Inflammatory Marker Neopterin.

Benefiting from the unique photoluminescence behavior of the lanthanide(III) ions and organic ligands, a lanthanide(III) metal-organic framework (Ln-MOF) material can simultaneously demonstrate photoluminescence of lanthanide(III) cations and organic molecules and endow its superior applications of fluorescence sensing behaviors. Herein, we present a europium(III) MOF material {[Eu(BPTA)·(CHCOO)·3DMA]·0.5DMA·3HO} () (where HBPTA is 3,3',5,5'-biphenyltetracarboxylic acid) for photoluminescence performance of quantitatively sensing the inflammatory marker neopterin (Neo). The obtained comprises Eu(COO) paddlewheel secondary building units, which could be bridged by BPTA ligands to extend a 2D framework. The fluorescence titration indicates can achieve simultaneous fluorescence behavior of Eu ions and Neo via on-off ratiometric effects and thus could be exploited as the ratiometric fluorescence sensor matrix. Such a fluorescence phenomenon of as a ratiometric sensor for quantitative detection of Neo via an on-off ratiometric effect is never observed in MOF chemistry. Moreover, naked-eye visible color variations of the fluorescence for could be observed from red to blue with increasing concentrations of Neo, confirmed by fluorescent test strips as well as portable fluorescent hydrogels. And also shows a low detection limit of 15.11 nM. A synergetic contribution of the competitive absorption, fluorescence resonance energy-transfer, and photoinduced electron-transfer mechanisms between Neo and the framework of realizes the on-off ratiometric fluorescence behavior for Neo detection, supported by the UV-vis spectral overlap experiment and DFT calculations.