A novel liquid crystal-based sensor for the real-time identification of organophosphonate vapors

In the current paper, we report the use of thin films of nematic liquid crystal (LC) 4-cyano-4′-biphenylcarbonitrile (5CB) supported on chemically functionalized surfaces as an optical sensor for detecting dimethyl methylphosphonate (DMMP) vapor. The surfaces were prepared by the deposition of copper perchlorate salts onto amino-terminated organic films with approximately 2 μm microgrooves assembled through the microcontact printing method. By exploring the LC orientation and the detection limit for DMMP vapor, we conclude that the copper perchlorate assembly time should be kept within 15–30 min. In the detection process, 5CB underwent transition from a homeotropic orientation to a tilted or planar one upon exposure to DMMP vapor because of the capture of the DMMP molecule by Cu2+. The optical signal generated by the LC orientation transition was easily identified using polarized light microscopy. The sensor exhibited high selectivity and its detection limit could reach to 0.51 mg/m3, demonstrating the feasibility of using these devices in the detection and positive identification of DMMP. Furthermore, the LC-based sensor reported in the current study did not require complex instrumentations, and the detection method was sufficiently simple.