An assessment of biological sensors for the detection of volatile compounds of forensic significance

Abstract

Olfaction, the sense of smell, provides the ability to assess environmental chemicals, which is crucial to the survival of numerous animals, including humans. The innate olfactory sensitivity and selectivity exhibited by animals has meant that there is immense interest in utilising their abilities in a range of applications, including forensic science. A comprehensive review of the published literature regarding the current and potential future uses of biological organisms as sensors for forensic applications highlighted the significant olfactory abilities of biological organisms. Also evident was the increasing interest in odorant receptors (ORs) – the biological components that impart olfactory ability – for detecting volatile compounds associated with odour spaces of forensic significance. This research was completed with the objective of assessing the feasibility of employing biological ORs as volatile compound sensors in forensic science. The feasibility assessment was composed of three primary studies. Firstly, the OR responses of the vinegar fly, Drosophila melanogaster, were investigated for the purpose of assessing their potential utility as sensors for volatile compounds associated with three distinct odour spaces: ignitable liquid residues, human decomposition, and living human scent. Secondly, a comprehensive examination of the olfactory system of Calliphora stygia was completed in order to investigate the potential utility of ORs from an organism for which the odour space of interest (human decomposition) is ecologically significant. Finally, an extensive examination of the antennal transcriptome of C. stygia was completed for the purpose of identifying members of the primary chemosensory gene families necessary for insect olfaction. The results obtained from this research clearly demonstrate that biological ORs could feasibly be employed for the detection of volatile compounds associated with odour spaces of forensic significance. A number of potential target compounds that could be exploited for the detection of the selected odour spaces were identified and, significantly, the identification, isolation, and functional characterisation of individual ORs that respond to some of those target compounds allowed for their respective response profiles, including their sensitivities and specificities, to be determined. Chemosensory genes, in addition to the odour-binding ORs that could potentially be employed for volatile compound detection purposes, were also identified. The assessment of D. melanogaster illustrated the different sensitivities, selectivities, and sensing features exhibited by individual ORs. For the first time, similar features were also identified in C. stygia ORs. This indicates that characteristics necessary for volatile compound detection are present within the ORs of these two organisms. The transcriptomic analysis of C. stygia antennae generated a comprehensive resource of candidate chemosensory proteins, in addition to ORs, that could also potentially be employed for detection purposes. Overall, the results of this research demonstrate the feasibility of employing isolated ORs for the detection of characteristic compounds in odour spaces of forensic significance. A number of avenues for further investigation were also provided. Further research expanding on this study will be required to demonstrate the performance characteristics that an OR-based sensor will ultimately possess; however, this research provides an encouraging first step towards the goal of utilising biological ORs as volatile compound sensors in forensic science.

Date of Award	2014
Original language	English
Supervisor	Alisha Anderson (Supervisor), Christopher Lennard (Supervisor) & Paul Kirkbride (Supervisor)