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Development of a selective electrostatic particle sampling system for the detection of trace explosives and illicit drugs

A selective sampling system for trace explosives and drugs
: Beer, Sebastian
: Wöllenstein, Jürgen; Wilde, Jürgen

Uelvesbüll: Der Andere Verlag, 2013, V, 178 S.
Zugl.: Freiburg/Brsg., Univ., Diss., 2013
Microsystem Simulation, Design and Manufacture, 9
ISBN: 978-3-86247-383-0
Fraunhofer IPM ()
gas sensor; sampling system; particle sampler

Trace detectors for explosives and illicit drugs are in development to meet the requirements of a wide range of security applications. For example, detection of trace explosives is necessary to quickly screen passengers in airports for bombs, and illicit drug detectors are required for transportation hubs as countermeasures to trafficking. The state of the art in these applications is the detection dog. However, while these dogs are able to detect with high sensitivity and selectivity, there are several drawback such as limitations in operating time and location. This has led to the ongoing development of alternative technologies for replacement of detection dogs. Presented in this thesis is the work in development of an air suction based particle sampling system. This system serves as an enabler to facilitate trace detection using gas sensors. While many of these sensors are in high technological readiness states, smart periphery like the presented sampler is required to allow for effective field operation. The particle sampler is based on an electrostatic particle precipitator (ESP), with an integrated heater for thermal desorption of the collected particles. The integration of the two functions is realized by a dual-use electrode design. In this arrangement, the unit is capable of collecting analytes in paniculate form, followed by thermal conversion into the vapor phase to facilitate gas detection. It is compatible with a wide range of gas detectors. This can lead to a handheld and field-ready detection system, if a low-power, miniaturized gas sensor is used. As an additional feature, the sampler is designed to selectively collect potential target analytes. Explosives commonly exhibit high electron affinity (EA) due to their nitro-groups, while the amine structure of drugs leads to high proton affinity (PA). The ESP can be designed to selectively precipitate high EA in the negative mode, while positive mode operation can feature selectivity toward high PA. With large portions of the background particle load exhibiting low EA and PA, these selective sampling modes allow for high collection rates for target analytes while discarding large portions of analytically irrelevant particles, thereby improving the gas detection analyte pool. Presented in this work is the relevant background information, a description of the demonstrator design process, an experimental evaluation of the sampler with regard to the collection efficiency and selectivity toward the target analytes, and a discussion of the results.