The successful air sampling and detection of cocaine, methylenedioxymethylamphetamine (MDMA), and marijuana using SPME-IMS achieved by targeting their volatile markers (methyl benzoate, piperonal, and terpenes, respectively) is presented. Conventional methods of direct air sampling for drugs are ineffective because the parent compounds of these drugs have very low vapor pressures, making them unavailable for headspace sampling. Instead of targeting the parent drugs, IMS was set at the optimal operating conditions (determined in previous work) in order to detect their volatile chemical markers. SPME is an effective and rapid air sampling technique for the preconcentration of analytes which is especially useful in confined spaces such as cargo containers, where the volatile marker compounds of drugs can be found in sufficient concentrations. By sampling the air using a 100 microm polydimethyl siloxane (PDMS) SPME fiber for as little as one minute, enough mass of the targeted volatile markers in the headspace of a quart-sized metal paint can (gallon, approximately 1101 cm(3)) which contained sub-gram quantities of the drug samples was recovered for IMS detection. Additionally, several potentially interfering compounds found in goods commonly shipped in cargo containers were tested individually as well as in mixtures with the drugs. No peak interferences were observed for MDMA or marijuana, and minimal peak interferences were found for cocaine.

This study demonstrates the use of solid-phase microextraction (SPME) to extract and pre-concentrate volatile signatures from static air above plastic explosive samples followed by detection using ion mobility spectrometry (IMS) optimized to detect the volatile, non-energetic components rather than the energetic materials. Currently, sample collection for detection by commercial IMS analyzers is conducted through swiping of suspected surfaces for explosive particles and vapor sampling. The first method is not suitable for sampling inside large volume areas, and the latter method is not effective because the low vapor pressure of some explosives such as RDX and PETN make them not readily available in the air for headspace sampling under ambient conditions. For the first time, headspace sampling and detection of Detasheet, Semtex H, and C-4 is reported using SPME-IMS operating under one universal setting with limits of detection ranging from 1.5 to 2.5 ng for the target volatile signatures. The target signature compounds n-butyl acetate and the taggant DMNB are associated with untagged and tagged Detasheet explosives, respectively. Cyclohexanone and DMNB are associated with tagged C-4 explosives. DMNB is associated with tagged Semtex H explosives. Within 10 to 60 s of sampling, the headspace inside a glass vial containing 1 g of explosive, more than 20 ng of the target signatures can be extracted by the SPME fiber followed by IMS detection.

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Ion mobility spectrometry (IMS) is routinely used in screening checkpoints for the detection of explosives and illicit drugs but it mainly relies on the capture of particles on a swab surface for the detection. Solid phase microextraction (SPME) has been coupled to IMS for the preconcentration of explosives and their volatile chemical markers and, although it has improved the LODs over a standalone IMS, it is limited to sampling in small vessels by the fiber geometry. Novel planar geometry SPME devices coated with PDMS and sol-gel PDMS that do not require an additional interface to IMS are now reported for the first time. The explosive, 2,4,6-trinitrotoluene (TNT), is sampled with the planar SPME reaching extraction equilibrium faster than with fiber SPME, concentrating detectable levels of TNT in a matter of minutes. The surface area, capacity, extraction efficiency, and LODs are also improved over fiber SPME allowing for sampling in larger volumes. The volatile chemical markers, 2,4-dinitrotoluene, cyclohexanone, and the taggant 4-nitrotoluene have also been successfully extracted by planar SPME and detected by IMS at mass loadings below 1 ng of extracted analyte on the planar device for TNT, for example.

New sensor technologies for homeland security applications must meet the key requirements of sensitivity to detect agents below risk levels, selectivity to provide minimal false-alarm rates, and response speed to operate in high throughput environments, such as airports, sea ports, and other public places. Chemical detection using existing sensor systems is facing a major challenge of selectivity. In this review, we provide a brief summary of chemical threats of homeland security importance; focus in detail on modern concepts in chemical sensing; examine the origins of the most significant unmet needs in existing chemical sensors; and, analyze opportunities, specific requirements, and challenges for wireless chemical sensors and wireless sensor networks (WSNs). We further review a new approach for selective chemical sensing that involves the combination of a sensing material that has different response mechanisms to different species of interest, with a transducer that has a multi-variable signal-transduction ability. This new selective chemical-sensing approach was realized using an attractive ubiquitous platform of battery-free passive radio-frequency identification (RFID) tags adapted for chemical sensing. We illustrate the performance of RFID sensors developed in measurements of toxic industrial materials, humidity-independent detection of toxic vapors, and detection of chemical-agent simulants, explosives, and strong oxidizers.