Detection of Olfactory Traces by Orthogonal Gas Identification Technologies - DOGGIES

摘要

Border security is one of the key challenges to be taken up by Europe in the following years. In particular, the deployment of practical efficient means to detect hidden persons and illegal substances at border crossing points is instrumental in avoiding terrorism, human trafficking or smuggling. This study presents the concept of an orthogonal" approach to the identification of gas traces identified as pertinent targets for illicit substances (drugs and explosives) as well as for human presence. The techniques employed to perform the analysis are based on completely different physical principles, these are the Mid-Infrared photo-acoustic spectroscopy (MIR-PAS - demonstration of a novel widely tunable integrated MIR source coupled with a miniature photo-acoustic cell) and the Ion mobility spectrometry (IMS) using a non radio-active ionization source. Definition of the pertinent compounds and their "spectral signature" (characterized with recording of the vapour phase IR properties via GC-FTIR and GC-MS), lead to a database of the target substances, the IR wavelengths were selected based on the individual target. For the case of human presence, volatile fatty acids (VFA) present in human sweat identified as ideal targets for remote detection of hidden persons, for example some VFAs are human specific, such as HMHA and 3MHA. The aforementioned VFAs are also active in the MIR range. Similarly for the case of the illicit drugs targeting has been based on their emitted VOCs depending on the type of substance (e.g. alkaloid drugs associated with their volatile degradation products etc), during this study, characterization of the cannabis markers lead to the identification of a new marker (under revision for European patent). For explosives substances volatile taggants are mainly associated with VOCs available during their preparation. In total 58 volatile organic compounds (VOCs) were identified in this study as candidates for the detection of Humans (31), Illegal Drugs - 19), and Explosives (13). The aforementioned spectral database has been employed for algorithm selection and training, the algorithms used were the Support Vector Machines (SVM), Partial Least Squares -- Discrimant Analysis (PLS -- DA) and the k -- Nearest Neighbour (KNN), the results are very promising reaching levels of matching during training up to 98%. These algorithms will fuse the data collected and analysed by the two powerful techniques selected as the components of this ? orthogonal ? approach to the detection of the aforementioned gas traces. Target specific cavitand receptors were developed for the pre-concentrator procedure that increase the concentration of the gas trace in quest. During this work, improvement to the pre-concentration configuration has reduced the required time for the pre-concentration procedure significantly (10s of seconds compared to several minutes), this is part of the novelties developed during this study. IMS studies for detection of human presence has shown very promising results, recording levels of human specific gas traces after 15 minutes of a human present in an area of 50m3. This is very important considering that in most cases the people illegaly immigrating are confined in much smaller spaces and for very much longer periods (most of the times are more than one person too) which leads to increased concentration and abundance of the related VOCs hence, the instrument will definetely perform better. A miniaturized MIR-PAS has been developed supported by an array of DFB-QCLs that allows for this instrument to be a portable solution for operators at border points, assisting their daily activities and increase their performance. This is a powerful and promising tool to detect a very wide range of volatile organic compounds (VOCs).