A Europium Complex Doped Silica Sol-Gel Thin Film for Detection of Trace Organophosphate Vapor
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Since the development of organophosphate (OP) nerve agents during World War II, rapid, effective detection of low concentration OP’s has been necessary. The Tokyo subway attacks of 1995, which killed twelve and injured thousands, demonstrated how vulnerable major cities are to chemical warfare agent (CWA) attacks. OP’s are dangerous neurodegenerative chemicals that inhibit the enzyme acetylcholinesterase (AChE). Exposure to powerful OP’s inhibits the metabolism of acetylcholine (ACh), a neurotransmitter, by AChE, leading to constant muscular contraction signaling, and eventual death. A novel hybrid thin film doped with a Europium complex sensitizer has been created for the low level detection of OP’s. The intensely luminescent complex, Eu(TTA)3Phen (TTA=2-thenoyltrifluoroacetone, Phen=1,10 Phenanthroline), was characterized by FTIR, SEM, and luminescence spectroscopy, and doped into a SiO2 matrix via the sol-gel method. Doped thin films were exposed to various concentrations of diisopropyl fluorophosphate (DFP), a Sarin mimic and the luminescence intensity quenching by DFP was measured as a function of time. The thin films exhibited rapid luminescence quenching in the presence of DFP due to a cooperative effort between sol-gel and Eu(TTA)3Phen complexes. DFP coordinated to the complex allowed silica hydroxyl groups to hydrolyze DFP. The products, diisopropyl phosphate and hydrofluoric acid, were able to dissociate, causing protonation of the TTA- ligand, quenching the luminescence.