Supersensitive Detection of Explosives by “Nanonose” Arrays

http://nano.tau.ac.il In the last decade there has been a great increase in the development of trace and ultra-trace explosive detection, mainly due to the globalization of terrorist acts, and the reclamation of contaminated land previously used for military purposes. In this regard, detection methods for traces of explosives continue to be plagued by their low volatility and thus, the analytical problem remains challenging1-6. One of the most commonly-used high explosives over the last 100 years is 2,4,6-trinitrotoluene (TNT), which poses not only a dire security threat, but also great environmental concern due to soil and water contamination. Thus, TNT is a suitable target analyte for chemical-sensing devices. Analytical procedures in use today for the trace detection of explosives typically involve collecting vapor samples and analyzing them with a sensitive method. Several methodologies have been reported for detecting TNT and other explosives. Although some reported methods are very sensitive and selective, most are rather, expensive, timeconsuming and require bulky equipment, tedious sample preparation and an expert operator. Furthermore, these systems cannot be miniaturized and automated or cannot perform high-throughput analysis. A successful chemical sensor for TNT, and any other explosives, must: (1) be extremely sensitive given that the vapor pressure of TNT at 25oC is 5.8x10-6 Torr (<10 ppb), and even lower for other commonly used explosives, such as RDX and HMX, with vapor pressures in the ppt and ppq levels, respectively, (2) be highly selective, eliminating both false positives and false negatives, (3) be robust and not prone to drift, (4) have the ability to be easily miniaturized for field application and (5) most important, be able to perform real-time high-throughput analysis based on arrays of multiple sensing elements. Nanowire-based field-effect transistors (NW-FETs) are powerful potential new sensors for the detection of chemical and biological species.7-12 Recently, extensive work has been carried out with the use of nanowire electrical devices for the simultaneous multiplexed detection of multiple biomolecular species of medical-diagnostic relevance, such as DNA and proteins. For NW sensors operated as FETs, the sensing Supersensitive Detection of Explosives by “Nanonose” Arrays