Quantitative detection of a simulant of organophosphonate chemical warfare agents using liquid crystals

The performance characteristics of liquid crystal (LC)-based sensors for detection of dimethylmethylphosphonate (DMMP), a representative organophosphonate compound and simulant of chemical warfare agent sarin, are presented. The equilibration coordination interaction among the aluminum ions on a surface, the cyano group in LCs, and the phosphoryl group in DMMP have been exploited to achieve sensitive, fast, and reversible sensor responses. Measurement of the response time of the sensor allows quantitative detection of an unknown concentration of DMMP with high accuracy. The strong coordination interaction between the cyano group present in the LC and the aluminum ions supporting the film of LC provides immunity to exposure to a number of potentially interfering compounds including high humidity. Exposure studies under varied temperature and humid conditions show a minimal effect on the sensor performance. Although the sensors stored at room temperature exhibited slightly diminished sensitivity, the sensors stored at 4 °C remained functionally stable for at least six months. These results combined with the ease of fabrication using the established processes, low cost associated with off-the-shelf components, and small foot print suggest that these LC-based sensors can form the basis of a new class of low cost, light weight, robust sensors for a number of detection applications.