Since the mid-1800s, dogs’ noses have been put to work tracking missing people and detecting drugs, explosives, and most recently, some types of cancer . Sniffer dogs are usually used in airports for explosive detection in luggage and on passengers, as well as in the military for rescue and landmine discovery. Training dogs, however, can be quite costly. The Transportation Security Administration (TSA), for example, provides Pittsburgh International Airport with $50,000 per dog per year to cover training and related expenses (see Fig. 1). Additionally, employing these talented animals comes as a package deal, for the dogs work as a team with their handlers, who typically work with the dogs for 6 to 8 years . Although some security specialists remain firm in their beliefs that no technology can “perform as well as the canines do,” the dogs can mistake clean luggage or cargo as hazardous, which can result in the unnecessary, lengthy, and costly evacuation of an entire terminal .
A Look at the Common Explosive TNT
Fido – A Fitting Name for an Electronic Nose
Understanding how dogs recognize odors has allowed scientists to develop detection devices based on this physiological process. One such device inspired by the canine nose and the process of odor detection via vapor detection is a chemical sensor called “Fido,” created by ICx TechnologiesTM (see Fig. 3) . Fido began as a research project for the Defense Advanced Research Projects Agency, a program launched to inspire the production of devices with mine and explosive detecting abilities comparable to that of a well-trained canine. Fido is comprised of a small glass capillary known as the Sensing Element, which is coated with amplifying fluorescent polymer (AFP) . Ambient air is drawn into the Sensing Element, and vapors are passed over the coating of AFP, a process similar to that of inhaled air passing over a dog’s olfactory epithelium towards their embedded sensory receptors. When the AFP molecules, called chromophores, are activated by light at a designated wavelength, the molecules fluoresce. However, when explosive molecules enter the tube and bind to the chromophores, they become rigid and bind to surrounding chromophores, forming a “molecular wire.” This process reduces, or quenches, the AFP molecule’s fluorescence by suppressing its excited, light-emitting state.
Other electronic “sniffers” use fluorescent polymers to detect odors or explosives but are less indicative of the presence of explosive material because only a single fluorescent molecule is quenched by the explosive molecule. In Fido’s case, when a molecule of AFP is bound by the attacking molecule, a chain reaction occurs, resulting in the joining of several chromophores to form a rigid “wire” that no longer produce visible fluorescence. Thus, the number of chromophores in Fido’s Sensing Element that can be quenched by one explosive molecule is greatly amplified . This reduction of light or fluorescence – acting as a stimulus similar to the binding of odorant molecules to an olfactory receptor in the canine nose – then causes the device’s photonic detector to send a signal to Fido’s electronic interface, alerting the user of danger. Despite ICx TechnologiesTM’s original intention to create a device to detect explosives chemically similar to TNT, studies have shown that Fido can also recognize other dangerous compounds including the often difficult to detect chemical PETN. Overall, Fido provides a cost-effective method for landmine detection, can be used for screening people and vehicles for explosive chemicals, and has been adapted for underwater detection in the device called the Fido SeaPup. Fido even detects explosives at concentrations as miniscule as 1 part per quadrillion !
Using MEMS to Detect Explosives
PETN and its Nemesis Nanosensor
-  Correa, Julio. (2011). ”The Dog’s Sense of Smell.” 1-3. Available: http://www.aces.edu/pubs/docs/U/UNP-0066/UNP-0066.pdf [Nov. 1, 2011].
-  Newton, Tom. “K-9 History: The Dogs of War!” Internet: http://community-2.webtv.net/Hahn-50thAP-K9/K9History/ [Oct. 30, 2011].
-  Fontaine, Tom. (July 12, 2010). “Feds want more bomb-sniffing dogs to protect travelers.” TribLive News. http://www.pittsburghlive.com/x/valleynewsdispatch/s_689988.html [Nov. 3, 2011].
-  “Dogs Can Still Do the Job, But May Get Competition.” (2005). Airport Security Report, 12 (13), 1-1. Available: http://search.proquest.com.libproxy.usc.edu/docview/195211429/ 132D07DF19517597194/18?accountid=14749 [Nov. 1, 2011].
-  “Trinitrotoluene – TNT.” Internet: http://www.ch.ic.ac.uk/vchemlib/mim/bristol /tnt/tnt_text.htm [Nov. 2, 2011].
-  MacDonald, Jacqueline, J.R. Lockwood, and John McFee. (2003). Alternatives For Landmine Detection. [Online]. Available: http://www.questia.com/PM.qst?a=o&d=102703617 [Nov. 3, 2011].
-  Penn State. (2009, February 13). “Better Artificial Nose Inspired By Sniffer Dogs.” ScienceDaily. Available: http://www.sciencedaily.com/releases/2009 /02/090213172533.htm [Oct. 30, 2011].
-  ICx Technologies. “Fido Explosives Detectors: Technical Overview.” Available: http://gs.flir.com/uploads/file/products/brochures/fido%20technical%20overview.pdf [Nov 3, 2011].
-  Yinon, Jehuda. (March 1, 2003). “Detection of Explosive by Electronic Noses.” Analytical Chemistry. 99-105. Available: http://pubs.acs.org/doi/pdfplus/10.1021/ac0312460 [Nov. 3, 2011].
-  Sample, Ian. (Nov. 4, 2010). “Why PETN explosive is hard to detect.” The Hindu. http://www.hindu.com/seta/2010/11/04/stories/2010110450711600.htm [Nov. 4, 2011].
-  Technische Universität Darmstadt. (2011, July 26). “Nano Sensor Detects Minute Traces of Plastic Explosives: Scientists Enable Inexpensive, Reliable Checks for Explosives.” ScienceDaily. Available: http://www.sciencedaily.com/releases/2011/07/110726092952.htm [Nov. 3, 2011].
-  Smiths Detection. (2011). “Ion Mobility Spectrometry (IMS).” Internet: http://www.smithsdetection.com/IMS.php [Nov. 4, 2011].
-  Central Intelligence Agency. (Nov. 10, 2011). The World Factbook: Transportation. Online: https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html [Dec. 1, 2011].
-  “Nano Sensor Detects Minute Traces of Plastic Explosives.” (July, 26 2011). Internet: http://www.tu-darmstadt.de/vorbeischauen/aktuell/ni_36032.en.jsp [Nov. 6, 2011].