Detection of organophosphorous nerve agents using liquid crystals supported on chemically functionalized surfaces

We report use of thin films of the nematic liquid crystal E7 supported on chemically functionalized surfaces to indicate the presence of vapors of the organophosphorous nerve agents sarin (GB), soman (GD), tabun (GA) and VX. The surfaces were prepared by the deposition of metal perchlorate salts onto carboxylic acid-terminated self-assembled monolayers. When using surfaces prepared from aluminum perchlorate salts, the nematic film of E7 underwent a transition from a perpendicular orientation to a tilted or planar orientation upon exposure to vapors of GB, GD, GA or VX generated from a small drop of agent placed on a piece of filter paper. The orientational transition of the liquid crystal was readily apparent as an optical signal that was visible to the naked eye. The agent VX, which has the lowest vapor pressure of these organophosphorous nerve agents (∼140 ppb), was reported by the liquid crystal within 60 s. The agents GB, GD, and GA, which have higher vapor pressures, triggered responses in the liquid crystal that were evident within 15 s, 15 s, and 60 s, respectively. By preparing surfaces from perchlorate salts of aluminum(III), zinc(II) and iron(III) it was possible to distinguish between GB, VX and either GD or GA, thus demonstrating the feasibility of designing surfaces patterned with metal salts to detect and positively identify chemical warfare agents.