Development of a Gas-phase Portable Explosive Sensing System

Abstract

This thesis reports the development of a gas phase portable explosive sensing system. Transducers with different principles are developed for nitro aromatic explosive sensing and their sensing performances are compared. Various receptor materials are tested and their sensing performances are compared with each other. Multiple sampler and preconcentrator designs are fabricated and examined. Finally, a portable explosive sensor system is developed with the preliminary experiment data and demonstrates semi field test. Synthetic materials, peptide receptor, ST are tested as candidate materials. Among them, Sulfonated tetrafluoroethylene (ST) shows extreme sensitivity for reliable dinitrotolune (DNT) sensing capability in a field environment as well as in a controlled testing. The sensing performance of ST is verified with a certified standard gas generator and a commercially available quartz crystal microbalance (QCM). DNT vapor at various concentrations, ranging from 1 to 100 ppb, is exposed to the ST-functionalized QCM surface. The frequency response of the ST-functionalized QCM is monitored in the presence of controlled DNT vapor. The overall sensitivity ranging from 1 to 100 ppb is –0.072 Hz/ppb and the sensitivity from 0 to 2 ppb range is about -0.44 Hz/ppb. In addition, ST shows excellent DNT selectivity in a control experiment with toluene. The ST-functionalized QCM does not respond to toluene at a toluene concentration of 120 ppm which is 1,200 times higher than the maximum concentration of DNT during the experiment mentioned above. Various sampler designs are compared. Canine and porcine nose inspires sampler design, leading to the sampler design that mimics animal nose structure. Both designs have merits and demerits. Canine type was better in spatial resolution, porcine type has better in sampling efficiency near a target object. Gas to liquid interfacing sampler is developed and studied. Various transducers are developed and examined. TMTs (thin membrane transducer), CNT-FET, QCM (quartz crystal microbalance) are tested. The QCM is selected for field applications because of its reliable gas phase detection. The performance of QCM is enhanced by miniaturization. The miniaturized quartz crystal was 49.2-fold smaller by volume than the crystal in the commercial setup. As a result, 76.2-fold sensitivity enhancement is achieved. Based on the preliminary test results, a portable explosive sensing devices are developed. The development process undergoes three stages of prototyping. The second and third prototype successively demonstrates their feasibility. Especially, the third prototype demonstrates a semi field test using a real field-mimicking setup. It shows distinguishable signal differences between a sand box with DNT buried and a sand box without DNT. Its sensitivity is -33.52 Hz/ppb and LOD is 0.66 ppb.