Fluorinated ZnFeIII Hollow Metal-Organic Framework as a 19F NMR Probe for Highly Sensitive and Selective Detection of Hydrogen Sulfide

Hydrogen sulfide (H2S) is considered as a highly toxic environmental pollutant and an important signal transmitter in physiological processes, and the selective and reliable detection of H2S is of great concern and remains challenging. Herein, we report a smart sensitive "off-on" F-19 NMR sensor for H2S by partially introducing a fluorinated ligand to construct a hollow dual metal-organic framework (MOF) nanosystem, F-ZnFeIII hMOF, in which the fluorinated ligand acts as the F-19 signal source but is initially quenched due to the strong paramagnetic relaxation enhancement (PRE) effect from neighboring Fe3+ nodes. Upon exposure to sulfide ions, reduction of Fe3+ to Fe2+ is specifically triggered, which attenuates PRE efficiency, thus turning on the F-19 NMR signal. The unique hollow MOF architecture benefits the mobility of F-19 atoms, thereby improving the response sensitivity. Meanwhile, the desirable H2S-sorption feature and appropriate redox potential of Fe3+/Fe2+ account for the favorable selectivity. The increase in the F-19 signal is linear with the concentration of sulfide in the range of 20 to 150 mu M with a detection limit of 2.8 mu M. The probe is well demonstrated by analyzing H2S in complex matrixes such as biological and foodstuff samples.