A water-stable zinc(II)-organic framework as an on-off-on fluorescent sensor for detection of Fe3+ and reduced glutathione

As an important biomarker, the level of reduced glutathione in serum is vital for human health. A novel 3D metal-organic framework with excellent photoluminescence properties, formulated as [Zn-3(TNB) (DPE)(2)]center dot 2H(2)O center dot DMF (1) (H-3 TNB = 4,4 ',4 ''-nitrilotribenzoic acid and DPE = 1,2-di(4-pyridyl)ethylene), was constructed by a solvothermal reaction. Complex 1 exhibits high water stability and pH stability in aqueous solution. It can detect Fe3+ and Pb2+ as a turn-off fluorescent probe in PBS solution with high sensitivity and selectivity. The detection limits for Fe3+ and Pb2+ are about 3.40 x 10(-7) M and 4.59 x 10(-7) M, respectively. Compared to Pb2+, Fe3+ has stronger oxidizability, and can be reduced to Fe2+ with the addition of a reductant, causing the fluorescence intensity of the Fe3+@1 system to significantly recover while that of the Pb2+@1 system has little change. Thus, the Fe3+@1 system exhibits a fluorescence turn-on signal after adding reduced glutathione (GSH) due to the reduction reaction, which indicates that complex 1 can be designed as an on-off-on fluorescent probe to detect Fe3+ ions and reduced GSH. The mechanism for fluorescence recovery is the elimination of the FRET process between Fe3+ and complex 1. In view of this reversible detection event, a two-input molecular logic gate was constructed. In addition, the on-off-on fluorescent sensor can be successfully applied to detection of reduced GSH in serum and fruits and vegetables with a high recovery range and low relative standard deviations (RSDs). To the best of our knowledge, this is the first example of a MOF-based probe for reduced GSH recognition by fluorescence on-off-on in PBS solution.

Automated summary

The novel metal-organic framework compound 1 can act as a phosphorescence probe to detect Fe3+ and Pb2+ in aqueous solutions, and can be designed as an on-off-on fluorescent probe for detecting Fe3+ ions and reduced glutathione (GSH) due to reduction reaction.