Wireless sensors and sensor networks for homeland security applications.

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.

Characterizing the gas phase ion chemistry of an ion trap mobility spectrometry based explosive trace detector using a tandem mass spectrometer.

A commercial-off-the-shelf (COTS) ion trap mobility spectrometry (ITMS) based explosive trace detector (ETD) has been interfaced to a triple quadrupole mass spectrometer (MS/MS) for the purpose of characterizing the gas phase ion chemistry intrinsic to the ITMS instrument. The overall objective of the research is to develop a fundamental understanding of the gas phase ionization processes in the ITMS based ETD to facilitate the advancement of its operational effectiveness as well as guide the development of next generation ETDs. Product ion masses, daughter ion masses, and reduced mobility values measured by the ITMS/MS/MS configuration for a suite of nitro, nitrate, and peroxide containing explosives are reported. Molecular formulas, molecular structures, and ionization pathways for the various product ions are inferred using the mass and mobility data in conjunction with density functional theory. The predominant product ions are identified as follows: [TNT-H](-) for trinitrotoluene (TNT), [RDX+Cl](-) for cyclo-1,3,5-trimethylene-2,4,6-trinitramine (RDX), [NO(3)](-) for ethylene glycol dinitrate (EGDN), [NG+NO(3)](-) for nitroglycerine (NG), [PETN+NO(3)](-) for pentaerythritol tetranitrate (PETN), [HNO(3)+NO(3)](-) for ammonium nitrate (NH(4)NO(3)), [HMTD-NC(3)H(6)O(3)+H+Cl](-) for hexamethylene triperoxide diamine (HMTD), and [(CH(3))(2)CNH(2)](+) for triacetone triperoxide (TATP). The predominant ionization pathways for the formation of the various product ions are determined to include proton abstraction, ion-molecule attachment, autoionization, first-order and multi-order thermolysis, and nucleophilic substitution. The ion trapping scheme in the reaction region of the ITMS instrument is shown to increase predominant ion intensities relative to the secondary ion intensities when compared to non-ion trap operation.

Estimating probabilistic confidence for mixture components identified using a spectral search algorithm.

Providing a confidence measure associated with the substance(s) identified in an unknown mixture by a spectral search technique is critical for non-expert users of devices and techniques based on spectroscopy. In this work, a technique for estimating probabilities associated with substances identified by spectral searching is described. In the proposed approach, a mixture analysis algorithm processes the spectrum of an unknown sample using a spectral library to generate a list of substances that may be present in the sample. The partial correlation of each of the substances in the list is then computed. The estimation of the probability is accomplished through a generalized linear model that converts the partial correlation values to a probability measure for each of the mixture components. The statistical properties of partial correlation allow probability estimation irrespective of whether a substance is present in a pure form or within a mixture. The technique was evaluated using both simulated and real Raman spectra of multi-component mixtures, and adequate performance was demonstrated.

Analysis of black powder by ion mobility-time-of-flight mass spectrometry.

Ion mobility-time-of-flight mass spectrometry (IM-TOFMS) was used to identify and correlate response ions associated with three black powder samples by mass and mobility. Vapors produced by thermal desorption of the black powders were ionized by a (63)Ni source; subsequent response ions were separated and identified using IM-TOFMS. The same response ions were found for each black powder regardless of geographic origin. The most intense mass and mobility peaks were attributed to ionic forms of sulfur allotropes ((32)S(n)(-), where n = 1-5). Vapor samples from GOEX black powder were also analyzed by two stand-alone ion mobility spectrometry systems, yielding an average reduced mobility value (K(o)) of 2.28 +/- 0.02 cm(2) V(-1) s(-1) for black powder across all three instruments.

Improved specific biodetection with ion trap mobility spectrometry (ITMS): a 10-min, multiplexed, immunomagnetic ELISA.

Enabling trace chemical detection equipment utilized in the field to transduce a biodetection assay would be advantageous from a logistics, training, and maintenance standpoint. Described herein is an assay design that uses an unmodified, commercial off-the-shelf (COTS) ion trap mobility spectrometer to analyze an immunomagnetic enzyme-linked immunosorbant assay (ELISA). The assay, which uses undetectable enzymatic substrates and ELISA-generated detectable products, was optimized to quantitatively report the amount of target in the sample. Optimization of this ELISA design retained the assay specificity and detection limit (approximately 10(3) E. coli per assay) while decreasing the number of user steps and reducing the assay time to 10 min (>9-fold decrease as compared to past studies). Also discussed are previously undescribed, independent substrate/enzyme/product combinations used in the immunomagnetic ELISA. These discoveries allow for the possibility of a quantitative, multiplexed, 10-min assay that is analyzed by the ion trap mobility spectrometer trace chemical detector.