A quantitative assessment of chemical techniques for detecting traces of explosives at counter-terrorist portals

Vapor Trace Collection and Direct Ultrasensitive Detection of Nitro-Explosives by 3D Microstructured Electrodes

The development of a rapid, sensitive, and selective real-time detection method for explosives traces may have an enormous impact on civilian national security, military applications, and environmental monitoring. However, real-time sensing of explosives still possesses a huge analytical hurdle, rendering explosives detection an issue of burning immediacy and an enormous current challenge in terms of research and development. Even though several explosives detection methods have been established, these approaches are typically time-consuming, need relatively large equipment, demand sample preparation, require a skilled operator, and lack the capability to do high-throughput real-time detection, thus strongly constraining their mass deployment. Here, we demonstrate the use of amino-modified carbon microfiber (μCF) working electrodes for ultrasensitive, selective, and multiplex detection of nitro-based explosives. Furthermore, our sensing method works at high sampling rates by a single electrode in a single detection cycle. We hereby present the first demonstration of porous μCF electrodes used for the simultaneous collection/preconcentration of explosive molecular species through direct air sampling, followed by the electrochemical detection of the surface adsorbed electroactive species. Our chemically modified μCF electrodes allow straightforward vapor-phase detection and discrimination of multiple nitro-based explosives directly from collected air samples. Hence, our sensing approach has been shown highly effective in the ultratrace detection of nitro-based explosives, under real-world conditions.

Detection of Contact Traces of Powdery Substances

The current practice in securing the contact traces of chemical substances taken from clothes belonging to a person suspected of manual handling explosives is focused on pockets and cuffs. The outerwear worn by people who had contact with fluorescent powders that simulate explosives and drugs was the subject of this study. Clothes were first exposed to the test substance for a period of time and then analyzed by fluorescence methods to determine the location of the highest quantity of traces. The results obtained from the study confirm that the areas with the highest concentration of powdery traces are different from those suggested by current forensic practice. They appear to be promising for a more efficient identification of the suspects involved in illegal manufacturing of drugs of abuse or explosives. Moreover, they may be helpful for developing the methodology for handling the evidence material in the forensic clothing examination process.

A facile strategy applied to simultaneous qualitative-detection on multiple components of mixture samples: a joint study of infrared spectroscopy and multi-label algorithms on PBX explosives

We combined infrared spectroscopy with multi-label algorithms to propose a facile yet efficient strategy to realize simultaneous qualitative-detection on multiple components of mixture explosives without pre-separation.

Simultaneous determination of multiple components in explosives using ultraviolet spectrophotometry and a partial least squares method

We used UV spectrophotometry and a chemometric method to develop a novel method for the simultaneous determination of multiple components in explosives.

Surface modification for the collection and identification of fingerprints and colorimetric detection of urea nitrate

Glass surfaces were modified with a combination of dyes and reagents to allow for the potential simultaneous recording of a detailed fingerprint and the detection of the explosive urea nitrate (UN), as a proof of principle of surface modification for simultaneous linking of identity to manipulation of explosives. By coating microscope slides with 9,10-diphenylanthracene (DPA), p-dimethylaminobenzaldehyde (p-DMAB) and p-dimethylaminocinnamaldehyde (p-DMAC), a colorimetric change was observed in the presence of UN, while revealing a fingerprint with enough resolution to isolate at least 10 minutiae. This is the first step in creating point-of-care devices capable of detecting low concentrations of explosives and drug metabolites and connecting them to a fingerprint.

Supersensitive fingerprinting of explosives by chemically modified nanosensors arrays

The capability to detect traces of explosives sensitively, selectively and rapidly could be of great benefit for applications relating to civilian national security and military needs. Here, we show that, when chemically modified in a multiplexed mode, nanoelectrical devices arrays enable the supersensitive discriminative detection of explosive species. The fingerprinting of explosives is achieved by pattern recognizing the inherent kinetics, and thermodynamics, of interaction between the chemically modified nanosensors array and the molecular analytes under test. This platform allows for the rapid detection of explosives, from air collected samples, down to the parts-per-quadrillion concentration range, and represents the first nanotechnology-inspired demonstration on the selective supersensitive detection of explosives, including the nitro- and peroxide-derivatives, on a single electronic platform. Furthermore, the ultrahigh sensitivity displayed by our platform may allow the remote detection of various explosives, a task unachieved by existing detection technologies.

Photoacoustic spectroscopy of surface adsorbed molecules using a nanostructured coupled resonator array

A rapid method of obtaining photoacoustic spectroscopic signals for trace amounts of surface adsorbed molecules using a nanostructured coupled resonator array is described. Explosive molecules adsorbed on a nanoporous anodic aluminum oxide cantilever, which has hexagonally ordered nanowells with diameters and well-to-well distances of 35 nm and 100 nm, respectively, are excited using pulsed infrared (IR) light with a frequency matching the common mode resonance frequency of the coupled resonator. The common mode resonance amplitudes of the coupled resonator as a function of illuminating IR wavelength present a photoacoustic IR absorption spectrum representing the chemical signatures of the adsorbed explosive molecules. In addition, the mass of the adsorbed molecules as an orthogonal signal for quantitative analysis is determined by measuring the variation of the localized, individual mode resonance frequency of a cantilever on the array. The limit of detection of the ternary mixture of explosive molecules (1:1:1 of trinitrotoluene (TNT), cyclotrimethylene trinitramine (RDX) and pentaerythritol tetranitrate (PETN)) is estimated to be ~ 100 ng cm(-2). These multi-modal signals enable us to perform quantitative and rapid chemical sensing and analysis in ambient conditions.

Recent advances and remaining challenges for the spectroscopic detection of explosive threats

In 2010, the U.S. Army initiated a program through the Edgewood Chemical Biological Center to identify viable spectroscopic signatures of explosives and initiate environmental persistence, fate, and transport studies for trace residues. These studies were ultimately designed to integrate these signatures into algorithms and experimentally evaluate sensor performance for explosives and precursor materials in existing chemical point and standoff detection systems. Accurate and validated optical cross sections and signatures are critical in benchmarking spectroscopic-based sensors. This program has provided important information for the scientists and engineers currently developing trace-detection solutions to the homemade explosive problem. With this information, the sensitivity of spectroscopic methods for explosives detection can now be quantitatively evaluated before the sensor is deployed and tested.

Surface-enhanced Raman scattering spectroscopy of explosive 2,4-dinitroanisole using modified silver nanoparticles

2,4-Dinitroanisole (DNAN) is being used as a replacement for 2,4,6-trinitrotoluene (TNT) as a less-sensitive melt-cast medium explosive than TNT. In this paper, we studied the surface-enhanced Raman spectroscopy (SERS) analysis of DNAN using Ag nanoparticles (AgNPs) modified by L-cysteine methyl ester hydrochloride. Due to the formation of a Meisenheimer complex between DNAN and the modifier, the modified AgNPs can detect 20 μg/L (0.2 ng) and 0.1 mg/L (1 ng) DNAN in deionized water and aged tap water, respectively. Three other chemicals (L-cysteine, N-acetyl-L-cysteine, and L-cysteine ethyl ester hydrochloride) were used as AgNPs modifiers to study the mechanism of the SERS of DNAN. It was confirmed that the amino group of L-cysteine methyl ester hydrochloride was the active group and that the methyl ester group significantly contributed to the high SERS sensitivity of DNAN. In order to further test the mechanism of Meisenheimer complex formation, the effect of anions and cations present in natural water on the SERS of DNAN was studied. It was found that CO(3)(2-), Cl(-), and K(+) at 100 mg/L did not negatively affect the SERS of 10 mg/L DNAN, while SO(4)(2-), Na(+), Mg(2+), and Ca(2+) at 100 mg/L significantly quenched the SERS of 10 mg/L DNAN. The negative effect of the bivalent cations could be offset by SO(4)(2-).

Ion spectrometric detection technologies for ultra-traces of explosives: a review

In recent years, explosive materials have been widely employed for various military applications and civilian conflicts; their use for hostile purposes has increased considerably. The detection of different kind of explosive agents has become crucially important for protection of human lives, infrastructures, and properties. Moreover, both the environmental aspects such as the risk of soil and water contamination and health risks related to the release of explosive particles need to be taken into account. For these reasons, there is a growing need to develop analyzing methods which are faster and more sensitive for detecting explosives. The detection techniques of the explosive materials should ideally serve fast real-time analysis in high accuracy and resolution from a minimal quantity of explosive without involving complicated sample preparation. The performance of the in-field analysis of extremely hazardous material has to be user-friendly and safe for operators. The two closely related ion spectrometric methods used in explosive analyses include mass spectrometry (MS) and ion mobility spectrometry (IMS). The four requirements-speed, selectivity, sensitivity, and sampling-are fulfilled with both of these methods.

A hybrid nanosensor for TNT vapor detection

Real-time detection of trace chemicals, such as explosives, in a complex environment containing various interferents has been a difficult challenge. We describe here a hybrid nanosensor based on the electrochemical reduction of TNT and the interaction of the reduction products with conducting polymer nanojunctions in an ionic liquid. The sensor simultaneously measures the electrochemical current from the reduction of TNT and the conductance change of the polymer nanojunction caused from the reduction product. The hybrid detection mechanism, together with the unique selective preconcentration capability of the ionic liquid, provides a selective, fast, and sensitive detection of TNT. The sensor, in its current form, is capable of detecting parts-per-trillion level TNT in the presence of various interferents within a few minutes.

Bioassays for bomb-makers: proof of concept

Clandestine bomb-makers are exposed to significant amounts of explosives and allied materials. As with any ingested xenobiotic substance, these compounds are subject to biotransformation. As such, the potential exists that characteristic suites of biomarkers may be produced and deposited in matrices that can be exploited for forensic and investigative purposes. However, before such assays can be developed, foundational data must be gathered regarding the toxicokinetics, fate, and transport of the resulting biomarkers within the body and in matrices such as urine, hair, nails, sweat, feces, and saliva. This report presents an in vitro method for simulation of human metabolic transformations using human liver microsomes and an assay applicable to representative nitro-explosives. Control and metabolized samples of TNT, RDX, HMX, and tetryl were analyzed using high-performance liquid chromatography coupled to tandem mass spectrometry (LC/MS/MS) and biomarkers identified for each. The challenges associated with this method arise from solubility issues and limitations imposed by instrumentation, specifically, modes of ionization.

Vibrational spectroscopy of triacetone triperoxide (TATP): anharmonic fundamentals, overtones and combination bands

The vibrational spectrum of triacetone triperoxide (TATP) is studied by the correlation-corrected vibrational self-consistent field (CC-VSCF) method which incorporates anharmonic effects. Fundamental, overtone, and combination band frequencies are obtained by using a potential based on the PM3 method and yielding the same harmonic frequencies as DFT/cc-pVDZ calculations. Fundamentals and overtones are also studied with anharmonic single-mode (without coupling) DFT/cc-pVDZ calculations. Average deviations from experiment are similar for all methods: 2.1-2.5%. Groups of degenerate vibrations form regions of numerous combination bands with low intensity: the 5600-5800 cm(-1) region contains ca. 70 overtones and combinations of CH stretches. Anharmonic interactions are analyzed.

The orientationally controlled assembly of genetically modified enzymes in an amperometric biosensor

A novel, nitroreductase (NTR) containing a sequence of six cysteine amino acids, enabling strong thiolate bonds to form on a gold electrode surface without the loss of enzyme activity, was genetically engineered. The enzyme was directly immobilised at a gold electrode without the need for pre-treatment of the surface with a self-assembled monolayer or a conducting polymer. The ensemble was used to develop an amperometric biosensor for the detection of explosives containing nitroaromatic compounds. Preliminary results demonstrate detection levels down to 100 parts per trillion, signifying tremendous promise towards an in situ sensor for the detection of explosives.

Molecularly imprinted polymers (MIPs): sensing, an explosive new opportunity?

Our group is currently developing in-field detection systems alongside the Australian Federal Police Forensic Services utilising molecularly imprinted polymers as the recognition elements. This review looks at MIP synthesis and our perceptions of future directions from an Australian and forensic perspective.

Molecularly Imprinted Polymers and Room Temperature Ionic Liquids: Impact of Template on Polymer Morphology

Molecularly imprinted polymers (MIPs) were generated for trans-aconitic acid 1 and cocaine 2 in a variety of porogens (CH3CN, CHCl3, [bmim][BF4], and [bmim][PF6]). MIP synthesis in either [bmim][BF4] or [bmim][PF6] resulted in significant acceleration of polymerization rates and, in the case of low temperature polymerizations, reactions were complete in less than 2 h, while no product was observed in the corresponding volatile organic carbon (VOC) porogen. In all instances, MIPs generated in [bmim][BF4] or [bmim][PF6] returned imprinting selectivities (I values) on par with or better than the corresponding MIP generated in VOCs. Imprinting values ranged between I = 1 and 2.9, with rebinding limited to 1 h. MIP synthesis conducted at low temperature (5°C) afforded the highest I values. Scanning electron microscopy examination of MIP morphology highlighted an unexpected template effect with MIP structure varying between discrete nanoparticles and robust monoliths. This template–monomer interaction was also observed in the rates of polymerizations with differences noted in reaction times for 1 and 2 MIPs, thus providing indirect conformation of our previously proposed use of molecular modelling–nuclear magnetic resonance titrations (the MM-NMR method) in the design phase of MIP generation. In addition, considerable batch-to-batch rebinding selectivities were observed.

Solid phase microextraction ion mobility spectrometer interface for explosive and taggant detection

Ion mobility spectrometry (IMS) is a rugged, inexpensive, sensitive, field portable technique for the detection of organic compounds. It is widely employed in ports of entry and by the military as a particle detector for explosives and drugs of abuse. Solid phase microextraction (SPME) is an effective extraction technique that has been successfully employed in the field for the pre-concentration of a variety of compounds. Many organic high explosives do not have a high enough vapor pressure for effective vapor sampling. However, these explosives and their commercial explosive mixtures have characteristic volatile components detectable in their headspace. In addition, taggants are added to explosives to aid in detection through headspace sampling. SPME can easily extract these compounds from the headspace for IMS vapor detection. An interface that couples SPME to IMS was constructed and evaluated for the detection of the following detection taggants: 2-nitrotoluene (2-NT), 4-nitrotoluene (4-NT), and 2,3-dimethyl-2,3-dinitrobutane (DMNB). The interface was also evaluated for the following common explosives: smokeless powder (nitrocellulose, NC), 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), 2,4,6-trinitrotoluene (2,4,6-TNT), hexahydro-1,3,5-trinitro-s-triazine (RDX), and pentaerythritol tetranitrate (PETN). This is the first peer reviewed report of a SPME-IMS system that is shown to extract volatile constituent chemicals and detection taggants in explosives from a headspace for subsequent detection in a simple, rapid, sensitive, and inexpensive manner.