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Indiana University-Purdue University Indianapolis (IUPUI) / Trained canines are commonly used as biological detectors for explosives; however, there are some areas of uncertainty that have led to difficulties in canine training and testing. Even though a standardized container for determining the accuracy of explosives-detecting canines has already been developed, the factors that govern the amount of explosive vapor that is present in the system are often uncertain. This has led to difficulties in comparing the sensitivity of canines to one another as well as to analytical instrumentation, despite the fact that this container has a defined headspace and degree of confinement of the explosive. For example, it is a common misconception that the amount of explosive itself is the chief contributor to the amount of odor available to a canine. In fact, odor availability depends not only on the amount of explosive material, but also the explosive vapor pressure, the rate with which the explosive vapor is transported from its source and the degree to which the explosive is confined. In order to better understand odor availability, headspace GC/MS and mass loss experiments were conducted and the results were compared to the Ideal Gas Law and Fick’s Laws of Diffusion. Overall, these findings provide increased awareness about availability of explosive odors and the factors that affect their generation; thus, improving the training of canines. Another area of uncertainty deals with the complexity of the odor generated by the explosive, as the headspace may consist of multiple chemical compounds due to the extent of explosive degradation into more (or less) volatile substances, solvents, and plasticizers. Headspace (HS) and solid phase microextraction (SPME) coupled with gas chromatography/mass spectrometry (GC/MS) were used to determine what chemical compounds are contained within the headspace of an explosive as well as NESTT (Non-Hazardous Explosive for Security Training and Testing) products. This analysis concluded that degradation products, plasticizers, and taggants are more common than their parent explosive.

Doctor of Philosophy / Department of Mechanical and Nuclear Engineering / William L. Dunn / The signature-based radiation scanning (SBRS) technique can be used to rapidly detect nitrogen-rich explosives at standoff distances. This technique uses a template-matching procedure that produces a figure-of-merit (FOM) whose value is used to distinguish between inert and explosive materials. The present study develops a tiered-filter implementation of the signature-based radiation scanning technique, which reduces the number of templates needed. This approach starts by calculating a normalized FOM between signatures from an unknown target and an explosive template through stages or tiers (nitrogen first, then oxygen, then carbon, and finally hydrogen). If the normalized FOM is greater than a specified cut-off value for any of the tiers, the target signatures are considered not to match that specific template and the process is repeated for the next explosive template until all of the relevant templates have been considered. If a target’s signatures match all the tiers of a single template, then the target is assumed to contain an explosive. The tiered filter approach uses eight elements to construct artificial explosive-templates that have the function of representing explosives cluttered with real materials. The feasibility of the artificial template approach to systematically build a library of templates that successfully differentiates explosive targets from inert ones in the presence of clutter and under different geometric configurations was explored. In total, 10 different geometric configurations were simulated and analyzed using the MCNP5 code. For each configuration, 51 different inert materials were used as inert samples and as clutter in front of the explosive cyclonite (RDX). The geometric configurations consisted of different explosive volumes, clutter thicknesses, and distances of the clutter from the neutron source. Additionally, an objective function was developed to optimize the parameters that maximize the sensitivity and specificity of the method.

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<p dir="ltr">Efficiently identifying commercial and improvised explosives is a crucial prerequisite for disarming and disposing of these dangerous materials. In conjunction with traditional techniques (e.g., ion mobility spectrometry and mass spectrometry), electrochemical sensors can function as low-form factor and inexpensive options to quickly identify chemical threats. In particular, organic electrochemical transistors (OECTs) have many attractive properties, and they have become viable options for biosensing. OECTs employ a simple geometry consisting of a conducting polymer active layer and an electrolyte controlled by a gate electrode. In turn, this provides a means for the solution-phase detection in short times. Here, the OECT architecture was extended to the challenge of explosive trace detection. These sensors were adapted to detect several families of explosives (i.e., acid-salts, nitroaromatics, nitroamines, nitrate-esters, and peroxides). Many of these sensors incorporated molecularly imprinted polymers (MIPs) to improve chemical selectivity. These MIPs were shown to introduce size exclusive properties to the OECTs, which can be leveraged to detect acid salts explosives. MIPs that were complementary to nitrated explosives (nitroaromatics, nitroamines, and nitrate-esters) also were prepared. These MIPs can adsorb their respective explosive decreasing their polymer porosity and ion-transport. Finally, a stand-alone OECT design was applied to detect peroxide-based explosives. These explosives were decomposed to hydrogen peroxide intermediates. The evolved hydrogen peroxide was then identified as it was electro-oxidized at the gate electrode. After establishing the viability of the discussed techniques, two new directions for designing OECT sensors were proposed. Finally, these two outlooks were combined as a potential strategy for directly detecting peroxide-based explosives. While only a small subset of explosives was considered, the strategies applied were not unique to these specific targets. Indeed, these OECTs detecting principles could be applied to a broader scope of explosives detection as well as novel chemical sensing horizons.</p>

With the goal of improving chemical detection methods for buried improvised explosive devices (IED’s), the intention of this study is to show that functionalized nano-particles improve the sensing properties of a polymer applied to gas sensors. The approach was reinforcing the polymer, Nafion, with acid-functionalized carbon nanotubes (CNT’s). Ammonia was chosen as the analyte for its similarity to IED byproducts without the dangers of toxicity or explosion. Two sensor platforms were investigated: Quartz crystal microbalances (QCM’s) and microcantilevers (MC’s). Preliminary evaluation of treated QCM’s, via frequency analyzer, showed improvements in sensitivity and fast reversal of adsorption; and suggested increased stability. Tests with coated MC’s also supported the findings of QCM tests. Amplitude response of MC’s was on average 4 times greater when the Nafion coating contained CNT’s. Quantitative QCM testing with gas-flow meters showed that with CNT inclusion: the average number of moles adsorbed increased by 35% (>1.2 times frequency response); sensitivity improved by 0.63 Hz/ppt on average; although the detection threshold decreased marginally; but reusability was much better after extended exposures to concentrated ammonia. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2013.

Ion mobility spectrometry is a powerful technique for the study related to molecule. The work of tow major applications are introduced in this paper. The first application is the optimization of parameters in CCS. The accurate calculation of the collision cross section for multiple molecules is a long-time interested topic in the research for substances detection in micro scale. No reliable analytical approach to calculate the collision cross section has been established to date. Different approaches rely on different mechanism will provide different results in significant extent. This work introduce a method for the determination of parameters in the Lennard Jones potential. Experimental data combined with numerical computation was the fundamental strategy during the optimization of the parameters. In the experiment, electrospray is used as the ion source of IMS while a nebulizer was utilized to electrify the aromatic compounds. New parameters show no less accuracy and equal efficiency while can explain the physical meaning of the collision more clearly. The second application is the trace detection of explosives with very low concentration. The detection of explosives is an important topic in security, while the detection will be difficult due to the low vapor pressure of explosives. In this work, two types of devices are designed for the trace detection of explosives at an extremely low concentration. TNT is selected as the explosives in the experiment. The experiment succeed to reach a sensitivity of 1 part per quintillion, and even find out a linear relationship between the logarithm of TNT concentration and TNT vapor pressure.

This thesis presents studies of organic semiconductor lasers, including their operation when pumped by a light-emitting diode (LED), and their application as explosive sensors. The photophysics and amplified spontaneous emission (ASE) of star-shaped oligofluorene truxene molecules were investigated. These materials exhibit high gain and low optical loss in thin-film waveguides. Low ASE thresholds were achieved with the truxene T3 and T4. Second-order distributed feedback (DFB) lasers were fabricated, with pump threshold intensities below 0.5 kW/cm² and broad tunability of the emission. DFB lasers were demonstrated with a novel polymer BBEHP-PPV, pumped by a pulsed commercial InGaN LED. The laser emission occurred at 533 nm for peak drive current above 15 A. The output beams and pulse-dynamics of the lasers were investigated for the first time, along with a 'double-threshold' phenomenon that was observed in this long-pulse pumping regime. BBEHP-PPV lasers based on various types of diffractive resonators were also fabricated by UV nanoimprint-lithography (NIL). By optimising the resonator design and the fabrication, and the pump-beam geometry, polymer laser thresholds of ~60 W/cm², the lowest recorded for NIL lasers, were demonstrated, enabling them to be pumped by pulsed commercial LEDs and custom micro-LED arrays. One promising application of organic lasers is in explosive sensing. A polymer of intrinsic microporosity (PIM-1) was used to detect nitroaromatic vapours. Rapid detection of dinitrobenzene (DNB) of low vapour pressure was achieved by monitoring the photoluminescence and laser emission during exposure. In addition, a CMOS time-resolved fluorescence lifetime microsystem with a commercial green-emitting copolymer was used as a novel, portable sensor to detect DNB vapour. An InGaN LED pumped BBEHP-PPV laser was also used as a miniature sensor to detect 10 ppb of DNB. These highly sensitive hybrid sensors could be used in humanitarian demining, complementing existing technologies leading to improvement in the detection of hazardous objects.