Explosive Trace Detection using Remote MIR Spectroscopy

The detection of hazardous and illicit substances, such as explosives, plays a key role in security applications. The technologies that are currently being used for such applications are terahertz scanners, ion mobility spectrometry and mass spectrometry (swipe tests) and canines.[1,2] All of these technologies are either unable to detect traces of explosives or they require time consuming sampling and a lot of ressources. Canines on the other hand are very sensitive and fast, but require frequent rests and training. All of those disadvantages may be overcome using midinfrared (MIR) laser spectroscopy. MIR spectroscopy allows for contactless and fast detection of explosives. As the detection is based on molecular vibrations, the method is highly selective. We have developed a system that uses a quantum cascade laser (QCL) to detect traces of explosives at distances between 50 cm and 2 meters. A recent study investigated the sensitivity of our system for the explosives pentaerythritol tetranitrate (PETN), hexogen (RDX), trinitrotoluene (TNT) and ammoniumnitrate (AN) on quartz surfaces. The results clearly show that we are able to detect amounts well below 100 ng of the named explosives at a detection distance of 1 m. Here, we will discuss the detection limit of our system as well as data analysis strategies and a road toward a detection algorithm for these substances. Challenges that arise during the analysis of more complex substrates than quartz, such as textiles, will also be adressed. [1] Glackin, J.M.E.; Gillanders, R.N.; Eriksson, F.; Fjällgren, M.; Engblom, J.; Mohammed, S.; Samuel, I.D.W.; Turnbull, G.A. “Explosives detection by swabbing for improvised explosive devices.” Analyst 2020, 145, 7956–7963. [2] Bauer, C.; Sharma, A.; Willer, U.; Burgmeier, J.; Braunschweig, B.; Schade, W.; Blaser, S.; Hvozdara, L.; Müller, A.; Holl, G. Potentials and limits of mid-infrared laser spectroscopy for the detection of explosives. Appl. Phys. B 2008, 92, 327–333