Odor signature evaluation: Perspectives encompassing explosives and pathogen detection



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Canines have been utilized as biological detectors for centuries due to their instinctual drive to detect scent given off by prey making them the perfect hunting companion to humans. As time and technology have progressed, the use of canines as a detector has been expanded well beyond the hunting of prey. Canines are now trained and utilized for detection purposes in a wide variety of fields including explosives, narcotics, contraband, living and deceased humans, agriculture, currency, pests, and more recently medical diagnostic fields. The superior detection ability of the canine can be attributed to the significantly complex olfactory epithelium which provides for a large surface area of olfactory receptors, while the structure of their nasal cavity provides for efficient odor transport allowing for enhanced sensitivity to odor. There has been extensive research and effort into developing programs within the various fields of canine odor detection for trainers, handlers, and their canines. However, there is still a gap in knowledge in understanding the chemical odor signature of target odorants that the canine is specifically using when displaying the alert. It is known that canines can discriminate between odors and are also able to generalize while still correctly identifying the trained odorant. While research is currently ongoing, there is still limited knowledge in the chemical characterization of the odorants, i.e., the volatile organic compounds (VOCs) that are present in target odor sources. With technological advancements in analytical chemistry, a variety of questions about chemical makeup and odor profiles have surfaced in a number of areas. It has been reported that the compound diphenylamine is a common stabilizer used in explosives and smokeless powders. Plastic explosives such as trinitrotoluene (TNT) and composition 4 (C-4) have a number of compound identifiers including 2-ethyl-1-hexanol (2E1H). The identification of these compounds in a post-blast scenario can aid in identification of explosive components used in improvised or homemade explosives and provide evidence that may assist in the identification of a suspect. However, identification of these components before detonation can prevent terrorist events and loss of life. Optimal methods for delivery output have been validated using an in-house olfactometer, while simultaneously monitoring target volatile odor signatures above the headspace of an array of explosive classes. A 13-month longevity and persistence evaluation of smokeless powder indicated an expected fluctuation in the target odor volatile concentration of diphenylamine during active canine trials. Additionally, throughout the longevity monitoring, analytical detection of the target odorant was absent among some sample points. These results demonstrate a necessity for enhanced olfactory-based behavioral tools when utilizing biological detectors as analytical detection. Given that canine performance did not decrease among sampling trials it is evident there is a combination of VOCs rather than individual compounds present in the canine response to the odor profile. With respect to pathogen detection, current research trends are exploiting chemical odor profiles for medical diagnostics, disease prevention, and routine therapeutic monitoring. Using the highly virulent Clostridium difficile (C. diff), which is associated with a severe nosocomial infection, this study explored the chemical odor signature of this target pathogen. This infection causes increasingly higher morbidity and mortality rates and is common among the elderly and immunocompromised. The individual odor profile can be altered by disease and stress in the body which can be potentially utilized for identification and diagnostic purposes. As canines are utilized as detectors with explosives and various medical diagnostics that include infection, identification of volatile odor signatures emanating from targets of canine detection relevance has become ever more important. This study focuses on the coupling of analytical chemistry with canine training materials to understand the unique odor profile of Clostridium difficile (C. diff) to develop a safe and effective training aid for medical detection canine teams. Studies assessed C. diff inoculated media via an indirect passive headspace adsorption onto a Getxent tube followed by a SPME-GC/MS instrumental evaluation to chemically characterize emitted odor signatures. Evaluation of the longevity of the novel training aid was also studied to discern the persistence of the target odorant. As the field of canine odor detection continues to expand in applications of homeland security and medical detection, research into the related target odorants must expand on an equal level. Understanding these compounds both individually and in a mixture is key in developing an expanded knowledge base of canine response to trained odors as well as safe and effective training aid development, enhanced standardization of the canine odor detection field, expanded utilization for homeland security purposes, practical application in medical detection and diagnostic as well as further solidification of the scientific foundation presented within the legal sector.



Explosive detection, Improvised explosive device (IED), Explosive odor profile, Volatile Organic Compound (VOC), Electronic detector, Biological detector, Homemade Explosive, Solid Phase Microextraction (SPME), Smokeless powder, Odor delivery