The abnormal concentration of anthrax spore biomarker 2,6-pyridinedicarboxylic acid (2,6-DPA) will seriously affect public health. Therefore, a sensitive and rapid assay for 2,6-DPA monitoring is of vital importance. In this work, novel nano-sized amorphous Eu-NH 2 BDC (amEu-NH 2 BDC) and amorphous Tb-NH 2 BDC (amTb-NH 2 BDC) metal organic frameworks are prepared by adjusting the ratio of metal and ligand, respectively. Both of them exhibit highly sensitive and selective ratiometric fluorescence detection for 2,6-DPA with wider linear range and lower detection limit in aqueous solutions and human serum. Attributed to the coordination effect of 2,6-DPA in triggering the characteristic fluorescence emissions of Eu 3+ or Tb 3+ by replacing coordinated solvent molecules, as evidenced by ultraviolet–visible spectroscopy, the fluorescence lifetimes analysis, thermal gravimetric analysis , Fourier-transform infrared spectroscopy, density functional theory (DFT) simulations and X-ray photoelectron spectroscopy. In addition, the amEu-NH 2 BDC or amTb-NH 2 BDC loaded paper-based microsensors are constructed for real-time and sensitive detection of 2,6-DPA and coupled with a smartphone-assisted visual portable device.
It is very crucial to develop a simple and fast-responsive sensor for the detection of water content in organic solvents . Herein, three different europium-organic frameworks (Eu-MOFs): amorphous Eu-2-aminoterephthalic acid (amEu-NH 2 BDC), crystalline Eu-2-aminoterephthalic acid (cryEu-NH 2 BDC) and amorphous Eu-1,4-benzenedicarboxylic acid (amEu-BDC) are synthesized, respectively. amEu-NH 2 BDC is employed as fluorescence probe for the determination of water in ethanol. Results indicate that amEu-NH 2 BDC exhibits good performance due to its dual-wavelength fluorescence (FL) with the ligand (NH 2 BDC)-centered blue luminescence at 430 nm and Eu-centered red luminescence at 615 nm. With the increase of water contents in ethanol, the emission intensity at 430 nm increases dramatically, while that at 615 nm decreases under a single excitation at 270 nm. By measuring the ratio of emission intensity at 430 nm and 615 nm (I 430 /I 615 ), a wide concentration range from 1% to 99.5% water in ethanol is obtained with a lower detection limit value of 0.024% (S/N = 3). Besides, in the presence of water in ethanol, the fluorescence color of amEu-NH 2 BDC changes from red to blue under 365 nm UV light. Thus, the visual device for the detection of water is realized by using amEu-NH 2 BDC. Combined with the fluorescence lifetime and density functional theory, it is shown that red luminescence weakens due to dynamic quenching and non-radiative vibration energy transfer, and blue luminescence is enhanced due to the hydrogen bonding between water and carboxyl groups in the ligand, which enhances the intramolecular charge transfer process. The proposed method has characteristics of rapid response, excellent stability, high sensitivity and selectivity. Importantly, it can be successfully applied to monitor the content of water in white spirit samples.
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