Achieving On–Off Ratiometric Luminescence Dynamics in a Nanoporous Eu(III) Metal–Organic Framework for Neopterin Detection

Thanks to the superior photoluminescence performance of the lanthanide(III) ions sensitized by the organic ligands via an "antenna effect" and the host–guest interactions between a MOF material and the targeted analytes, a nanoporous lanthanide(III) MOF material can achieve the luminescence dynamics performance through the influence of lanthanide(III) ions and the targeted analytes, thus endowing a nanoporous lanthanide(III) MOF material with superior ratiometric luminescence sensing application. Consequently, a 3D nanoporous Eu(III) based MOF material, {[Eu(BPDC)(μ3–OH)(H2O)]·H2O·DMF}n (Eu-MOF, 2,2′-bipyridine-4,4′-dicarboxylic acid = H2BPDC), assembled by H2BPDC ligand and Eu3+ ions for achieving on–off ratiometric luminescence dynamics performance of inflammatory marker neopterin (Neo) detection, has been fabricated. The nanoporous Eu-MOF material is consist of 1D Eu(μ3–OH) chains, which could further be connected by the deprotonated H2BPDC ligands to build a 3D framework, showing a nanosized aperture of ca. 12.6 Å × 12.6 Å along the a-direction. The luminescence titration experiments demonstrate that Eu-MOF can exhibit simultaneous photoluminescence behavior of Eu3+ ions and Neo, and achieve on–off ratiometric luminescence dynamics performance by regulating the host–guest interactions. More importantly, the visible color change observation from red to bluish violet by the naked eyes in response to the concentrations of Neo can be an indicator of facile Neo detection, achieved by luminescent test strips and portable hydrogels. A combination of competitive absorption and host–guest interactions between Eu-MOF material and Neo can contribute to on–off ratiometric luminescence dynamics performance of Eu-MOF material for Neo detection, confirmed by UV–vis spectral overlap experiment and density functional theory calculations.