Fast Response-Recovery and High Selectivity Chemicapacitive Detection of a Nerve Agent Simulant Vapor

Early detection of chemical warfare agents (CWAs) is critical in minimizing the exposure to chemical threats. This study presents a fast response-recovery chemicapacitive sensor (chemicapacitor) for a nerve agent simulant, dimethyl methylphosphonate (DMMP), with high selectivity and sensitivity. Chemicapacitors with interdigitated electrodes were fabricated on a SiO2/Si wafer by aligning single-walled carbon nanotubes (SW-CNTs) coated with polyhedral oligomeric silsesquioxane-supported 1,1,1,3,3,3-hexafluoro-2-propanol (POSS-HFIP) receptors. The stable, nano-sized three-dimensional structure with multiple terminal alcohol groups played a crucial role as a high-performance receptor via efficient hydrogen-bonding interaction with the CWA simulant. The response and recovery times of the fabricated chemicapacitors were estimated to be 13 and 88 s, respectively, outperforming chemiresistive sensors in terms of response-recovery dynamics. The capacitive responses were obtained at varying DMMP vapor concentrations, ranging from 25 to 150 ppm, and they exhibited superior sensitivity compared to receptor-free sensor devices. The concentration-dependent sensitivity was well-fitted with the Langmuir isotherm model, indicating that the sensing mechanism is based on the adsorption/desorption process. In addition, excellent selectivity was realized by introducing different toxic molecules (sulfur dioxide, ammonia, and ethylene oxide) and a blood agent (cyanogen chloride), where the fabricated POSS-HFIP/SW-CNTs chemicapacitor selectively responded to the DMMP vapor. The limit-of-detection was calculated to be 0.70 ppm. The proposed POSS-HFIP/SW-CNTs chemicapacitor demonstrated rapid response-recovery characteristics (with improved selectivity towards DMMP), suggesting its potential in reducing casualties or injuries by early identification of CWAs.