Polymer sensors for nitroaromatic explosives detection Sarah J. Toal and William C. Trogler* Received 19th December 2005, Accepted 6th April 2006 First published as an Advance Article on the web 27th April 2006 DOI: 10.1039/b517953j Several polymers have been used to detect nitroaromatic explosives by a variety of transduction schemes. Detection relies on both electronic and structural interactions between the sensing material and the analyte. Quenching of luminescent polymers by electron deficient nitroaromatic explosives, such as trinitrotoluene, may be monitored to detect explosives. Resistive sensing using carbon black particles that have been coated with different organic polymers and deposited across metallic leads can also be used to detect nitroaromatic vapors in an electronic nose approach. Frequency changes in surface acoustic wave devices may be monitored to detect nitroaromatics after their adsorption into polymer coatings. Luminescent polymetalloles have recently been investigated for sensing explosives in aqueous-based solutions and for improved visual detection of trace particulates on surfaces. 1. Introduction Chemical sensors for the rapid detection of explosives are important because they have important potential applications, such as tactical and humanitarian demining, remediation of explosives manufacturing sites, 1 and forensic and criminal investigations. 2,3 Homeland security applications are attract- ing increased research, because terrorists frequently employ explosive bombs. Various methods of explosives detection are currently available, but many simple techniques are often inefficient. Metal detectors are commonly used as an indirect technique for sensing explosive devices packaged in metal. This method is valuable for certain applications, such as for landmine and weapon detection, although many modern landmines employ plastic casings. Metal detectors, however, are not useful for other applications, such as for explosives screening in airports. Canines are considered the most reliable tool for the detection of explosive vapors; however, this method is expensive and not well-suited for continuous monitoring, because dogs require care and are easily fatigued. 4 Some methods, though highly sensitive, are expensive and require sophisticated instrumentation that is not easily applied to on-site field testing. Some such methods include gas chromatography coupled with mass spectrometry, 5 surface enhanced Raman spectroscopy, 6 nuclear quadrupole reso- nance, 7 energy dispersive X-ray diffraction, 8 neutron activa- tion analysis, electron capture detection, 1 and cyclic voltammetry. 9 Ion mobility spectrometry (IMS), which is a commonly used explosive detection system in airports, has sensitivity in the picogram to nanogram range, but it is also expensive, operator dependent, prone to false positives, and spectrometers must be frequently calibrated. 10 A review of instrumentation for trace explosives detection has been published recently. 11 High explosives consist of an intimate mixture of a chemical oxidant and reductant that on initiation undergoes a highly exothermic decomposition to yield gaseous products. Several nitroaromatic explosives are known, such as trinitrotoluene (TNT), tetryl, and picric acid. Mixtures of high explosives are also commonly used, and TNT, an inexpensive compound, is a component found in fifteen explosive compositions. 12 For example, TNT and dinitrotoluene (DNT) are widely used in Department of Chemistry and Biochemistry, University of California, San Diego, 9500 Gilman Dr., La Jolla, CA 92093-0358, USA. E-mail: wtrogler@ucsd.edu Sarah J. Toal Sarah J. Toal received a B.S. in Chemistry in 2000 and a B.A. in Philosophy in 2001 from the University of California, Irvine. She gradu- ated with a Ph.D. from the University of California, San Diego in December 2005. She was awarded an Achievement Rewards for College Scientists Scholarship from 2002–2005. William C. Trogler William C. Trogler received a B.A. from Johns Hopkins in 1974 and a Ph.D. from the California Institute of Technology in 1997, and has been a member of the UCSD faculty since 1983. He was elected a Fellow of the American Association for the Advancement of Science in 1988. FEATURE ARTICLE www.rsc.org/materials | Journal of Materials Chemistry This journal is ß The Royal Society of Chemistry 2006 J. Mater. Chem., 2006, 16, 2871–2883 | 2871