Nerve agents are highly toxic chemical warfare agents that inhibit acetylcholinesterase (AChE) in the nervous system, causing severe symptoms like seizures and respiratory failure. Timely detection of these agents is crucial to protect human health. 

Current detection methods include liquid chromatography-mass spectrometry (LC-MS), ion mobility chromatography, and fluorescence techniques. Fluorescence sensing is promising due to its ease of use and on-site applicability, primarily relying on the phosphorylation of nerve agents or protonation of probe molecules. However, environmental interferences can limit effectiveness, highlighting the need for rapid and reliable fluorescent sensing technologies for early warning of nerve agent exposure.

To address these limitations, a research team led by Prof. DOU Xincun from the Xinjiang Technical Institute of Physics and Chemistry of the Chinese Academy of Sciences, has developed a novel dual-sieving strategy based on chemical activity and molecular dimensions for detecting phosphonyl fluoride nerve agents.

The researchers utilized a zirconium-based metal-organic framework (MOF), MOF-525, as the sensing material. MOF-525, which features porphyrin ligands and zirconium clusters as metal nodes, exhibits high stability and resistance to acidic and basic conditions. By precisely modulating the amount of structural modulators, the researchers synthesized a series of MOF-525 materials with varying defect levels. Optimizing the modulator concentration resulted in a material with a high defect density (~60% defect rate) and minimal background fluorescence, enabling selective pore sieving for phosphonyl fluoride nerve agents based on their molecular size.

When the defect-engineered MOF-525 interacts with phosphonyl fluoride nerve agents, it triggers a distinct red fluorescence signal. This dual-sieving strategy, combining molecular size exclusion and chemical activity, allows the material to effectively distinguish phosphonyl fluoride nerve agents from structurally similar compounds. The optimized MOF-525 demonstrated exceptional performance, including high sensitivity (0.96 nm/3.8 ppb), rapid response (<1 second), and robust resistance to interferences from acidic substances, humidity, and common fluorescent materials.

This study not only elucidates the impact of defect engineering on the optical properties of MOFs but also establishes a new paradigm for the detection and recognition of trace nerve agents. The findings, published in Advanced Functional Materials, were supported by the National Key Research and Development Program of China and the Tianshan Innovation Team Plan. 

Figure: Defect Engineering Zr-MOF-Endowed Activity-Dimension Dual-Sieving Strategy for Anti-acid Recognition of Real Phosphoryl Fluoride Nerve Agents (Image by Prof. DOU’s group)