Electronic Noses & Sensors for the Detection of Explosives

Abstract

Trace-based explosives detection (ETD) systems currently in use have limitations in selectivity, sensitivity, size, and certainly cost (approximately $25,000 – $100,000+). Miniaturization of systems to bench top or even handheld levels has great potential, but these systems will still be limited in operation and perhaps only a quarter of the price of present day systems. The use of electronic-based sensors, based on microelectromechanical systems, MEMS, and even further in the future, nanotechnology based systems (or nano-electromechanical systems, NEMS), shows promise for large improvements in sensitivity, selectivity, improved alarm rates, size and cost (from approximately $1,000 to $25 each unit). With current events and emphasis in antiterrorism, there is a need to quickly develop and deploy systems to all airports, along with numerous other transportation modes, protection of government facilities, public facilities, schools, etc. This could be realized with low cost miniaturized electronic chemical detection systems, with the capability of detecting trace explosives, but also could include chemical and biological agent detection systems, as well as, hazardous chemical detection systems. This paper will provide an emphasis on the analytical challenges of trace explosives detection, including contamination studies, sample collection, preconcentration, and sensors for low level detection. ETD systems operate via the collection of small residues of particles and/or vapours that indicate larger quantities of explosives present in the object or environment. To appropriately analyze for traces of explosives, improvised explosive devices (IED) are fabricated in various manners and the contamination spread from these IEDs are measured by trace analytical instruments. This assists in establishing our specification or threshold levels, while at the same time permits the development of trace standards which simulate real IEDs in particle composition and calibrated levels. The current types of trace detection techniques presently deployed include ion mobility spectrometry, chemiluminescence and canines. Strengths and weaknesses of these ‘systems’ provide directional guides for future development of electronic sensors.