Trace Detection Of Explosives Research Articles

Current Trends and Challenges in Explosives Detection using Nanotechnology

Objective: This article highlights the applications of nanotechnology in the detection of explosives. Evidence acquisition: The increasing rise in terrorist acts throughout the globe has brought attention to the significance of locating hidden bombs and motivated new propelled breakthroughs to ensure public safety. Recognizing explosives and closely related-threatening combinations has already risen to the top of the priority list for contemporary national security and counterterrorism applications. Sensors based on nanotechnology have a fair probability of fulfilling all the criteria needed to be a practical solution for explosive trace detection. Results: Nanowire/nanotube, nanomechanical devices, and electronic noses are three nanosensor technologies that have the most potential to develop into commercially viable technology platforms for the detection of trace explosives. Certain functionalized nanoparticles can exhibit different behaviors as a result of unique interactions with nitroaromatics. Semiconducting singlewalled carbon nanotubes (SWCNT) have been used as wearable chemical sensors. Conclusion: In this paper, the potential of nanosensors has been exposed that can be used to build a sensor system with high selectivity and sensitivity and appropriate platforms for signal transduction for the detection of explosives.

Sensitive Detection of Trace Explosives by a Self-Assembled Monolayer Sensor.

Fluorescence probe technology holds great promise in the application of trace explosive detection due to its high sensitivity, fast response speed, good selectivity, and low cost. In this work, a designed approach has been employed to prepare the TPE-PA-8 molecule, utilizing the classic aggregation-induced emission (AIE) property of 1,1,2,2-tetraphenylethene (TPE), for the development of self-assembled monolayers (SAMs) targeting the detection of trace nitroaromatic compound (NAC) explosives. The phosphoric acid acts as an anchoring unit, connecting to TPE through an alkyl chain of eight molecules, which has been found to play a crucial role in promoting the aggregation of TPE luminogens, leading to the enhanced light-emission property and sensing performance of SAMs. The SAMs assembled on Al2O3-deposited fiber film exhibit remarkable detection performances, with detection limits of 0.68 ppm, 1.68 ppm, and 2.5 ppm for trinitrotoluene, dinitrotoluene, and nitrobenzene, respectively. This work provides a candidate for the design and fabrication of flexible sensors possessing the high-performance and user-friendly detection of trace NACs.

Synthesis of Novel Fluorescent Conjugated Polymers and Their Rapid Gas‐Phase Detection of Trace Nitro‐Explosives

AbstractFluorescent conjugated polymers are widely investigated for their excellent performance in detecting explosives. In this work, two simple monomers are used to synthesize two novel fluorescent conjugated polymers, 3 and 6, with different conjugated structures via the linkages of “single bond” and “alkyne bond” by coupling reaction, and the fluorescence sensing performance for 2,4,6‐trinitrotoluene (TNT) is verified in both liquid and gas phases, aiming to demonstrate the influence of two different linkages on the fluorescence sensing properties. The fluorescent intensities of conjugated polymers in organic solvents gradually increase with increasing concentration within the low concentration range, while too high concentration leads to a decrease in the emission intensity because of the concentration quenching effect. The liquid‐phase limit of detection of 3 and 6 for TNT is as low as 1.9 and 1.6 µm in acetonitrile, respectively. The change rule of UV–vis absorption indicates that the static quenching model of TNT is predominant in liquid phase. Using a commercial portable explosives detector, 3 and 6 can effectively achieve the selective detection of gas‐phase TNT above 15 ng within 7 s and 8 ng within 5 s, respectively, demonstrating the great potential for rapid on‐site detection of trace explosives.

Development of lycopene-based whole-cell biosensors for the visual detection of trace explosives and heavy metals

Residual explosives in conflicting zones have caused irreversible damage to human safety and the environment. Whole-cell biosensors can to detect remnants of buried explosives, such as 2,4-dinitrotoluene (DNT), a stable and highly volatile compound in explosives. However, all the reported whole-cell biosensors utilize fluorescence or luminescence as the biological markers, making their detection difficult in real minefields. Here, we presented a lycopene-based whole-cell biosensor in Escherichia coli to output visible signals in response to DNT, which can help in the visual detection of buried explosives. To construct the whole-cell biosensor, the DNT-responsive promoter yqjF was used as the sensing element, and the lycopene synthetic gene cassette crtEBI was served as the reporting element. Then, the metabolic flux for lycopene production was enhanced to improve the output signal of the whole-cell biosensor, and a terminator was utilized to reduce the background interference. The optimized biosensor LSZ05 could perceive at least 1 mg/L DNT. The DNT-specificity and robust performance of the biosensor under different environmental factors were confirmed. Our results showed that converting the biosensor into a lyophilized powder was an effective storage method. The biosensor LSZ05 could effectively detect DNT in two kinds of soil samples. The lycopene-based whole-cell biosensor could also be used to visually detect heavy metals. Our findings laid the foundation for visually detecting buried explosives in minefields, which was a valuable supplement to the reported biosensors. The methods used for optimizing the lycopene-based whole-cell biosensor, including the improvement of the output signal and reduction of background interference, were quite effective.

Stationary Explosive Trace Detection System Using Differential Ion Mobility Spectrometry (DMS).

Detecting trace amounts of explosives is important for maintaining national security due to the growing threat of terror attacks. Particularly challenging is the increasing use of homemade explosives. Therefore, there is a constant need to improve existing technologies for detecting trace amounts of explosives. This paper describes the design of a stationary device (a gate) for detecting trace amounts of explosives and explosive taggants and the design of differential ion mobility spectrometers with a focus on the gas system. Nitromethane (NM), trimeric acetone peroxide (TATP), hexamine peroxide (HMTD), and explosive taggants 2,3-dimethyl-2,3-dinitrobutane (DMDNB) and 4-nitrotoluene (4NT) were used in this study. Gate measurements were carried out by taking air from the hands, pocket area, and shoes of the tested person. Two differential ion mobility spectrometers operating in two different modes were used as explosive detectors: a mode with a semi-permeable membrane to detect explosives with high vapor pressures (such as TATP) and a mode without a semi-permeable membrane (using direct introduction of the sample into the measuring chamber) to detect explosives with low vapor pressures (such as HMTD). The device was able to detect trace amounts of selected explosives/explosive taggants in 5 s.

Fluorescent Materials Containing Polycyclic Aromatic Compounds: synthesis, Fluorimetric Detection of Nitroaromatic Compounds and Color Properties

Schiff bases with pyrene, anthracene or naphthalene groups can act as simple, sensitive, and selective sensors for the detection of trace explosives. We have prepared three new types of Schiff bases with fluorescent properties as fluorescent probes for use in the fluorescence detection of explosives. The detection properties of the synthesized compounds of photophysical and fluorescent explosives were investigated. Spectroscopic methods were used for the structural characterization of the compounds. Within the scope of the study, compounds (A, B and C) were used as fluorescent probes in the detection of some explosives and the data obtained were recorded. Instead of the quenching effect expected by the explosives on the emissions of the compounds, it was observed in some experiments that the emission intensity due to aggregation increased. In addition, the color measurements (CIE standards) and Color temperature (CCT) of the compounds were calculated.

Laser ablation synthesis of bimetallic gold-palladium core@shell nanoparticles for trace detection of explosives

Laser ablation synthesis of bimetallic gold-palladium core@shell nanoparticles for trace detection of explosives

Rapid Detection of Trace Nitro-Explosives under UV Irradiation by Electronic Nose with Neural Networks.

The development of an electronic nose (E-nose) for rapid explosive trace detection (ETD) has been extensively studied. However, the extremely low saturated vapor pressure of explosives becomes the major obstacle for E-nose to be applied in practical environments. In this work, we innovatively combine the decomposition characteristics of nitro explosives when exposed to ultraviolet light into gas sensors for detecting explosives, and an E-nose consisting of a SnO2/WO3 nanocomposite-based chemiresistive sensor array with an artificial neural network is utilized to identify trace nitro-explosives by detecting their photolysis gas products, rather than the explosive molecules themselves or their saturated vapor. The ultralow detection limits for nitro-explosives can be achieved, and the detection limits toward three representative nitro-explosives of trinitrotoluene, pentaerythritol tetranitrate, and cyclotetramethylene tetranitroamine are as low as 500, 100, and 50 ng, respectively. Moreover, by extracting the features of sensor responses within 15 s, a classification system based on convolutional neural network (CNN) and long short-term memory network (LSTM) is introduced to realize fast and accurate classification. The 5-fold cross-validation results demonstrate that the CNN-LSTM model exhibits the highest classification accuracy of 97.7% compared with those of common classification models. This work realizes the detection of explosives photolysis gases using sensor technology, which provides a unique insight for the classification of trace explosives.

Effect of evaporation on the limit of detection of explosive traces by active spectral imaging

When developing methods for standoff detection of explosive traces, an important issue is determination of the limit (minimum) amount of a substance available for detection. This limit depends on the features of the measuring complex realization, on the physicochemical properties of the substance, and on the dynamics of sublimation (evaporation) of the substance from the surface. In this work, we consider the problem of detection limit for a measuring complex based on the method of active spectral imaging. In realization of this method, the distance to the object and the measurement time after the appearance at the surface of a substance imprint are important. How long this trace amount of substance can be detected, taking into account its evaporation? An explosive imprint is a thin layer on a surface (usually considered as a fingerprint with traces of the substance). We theoretically consider the dynamics of the change in the area of this imprint on the basis of a mathematical model of evaporation of a thin layer. Based on mathematical modeling, we can estimate the amount of a specific substance available for detection under the given conditions and the availability time. We identified the main parameters that affect the rate of film evaporation and the range of parameter change and calculated the kinetic parameters of sublimation of thin films of some explosives. The performed calculations allowed us to draw conclusions about the detection limit of substances for the active spectral imaging method depending on the distance to the measurement object and the time after the appearance of a surface trace with an initial surface concentration and area specific to a fingerprint.

Trace Explosive Detection Based on Photonic Crystal Amplified Fluorescence.

With increasing demand for public security and environmental protection, it is highly desirable to develop strategies to identify trace explosives (e. g., 2,4,6-trinitrotoluene (TNT)). Herein, we report novel photonic crystal (PC)-based sensor chips for trace TNT detection by using amplification effect of PCs on fluorescence (FL) signals. The sensor chips are constructed by integrating silica nanoparticles (NPs) modified with (3-aminopropyl)triethoxysilane (APTES) and fluorescein isothiocyanate isomer (FITC) and PC substrates. The amino groups on FITC-APTES-silica NPs can specifically bind with TNT molecules to form Meisenheimer complexes and strongly quench the FL signal of neighboring fluorophores FITC through Förster resonance energy transfer. PCs with matched PBG can amplify the FL signal of FITC-APTES-silica NPs about 24.4-fold and significantly improve sensitivity and resolution of trace TNT detection with the limit of detection of 0.23 nM. The PC-based sensor chips are stable, sensitive, and reliable TNT sensing platforms, showing great potential in homeland safety and environmental protection.

Thermal control of organic semiconductors for trace detection of explosives.

Organic semiconductors can be applied as ultra-sensitive fluorescent sensors for detecting trace vapours of explosives. The detection of explosives is manifest by the fluorescence quenching of the sensors. However, for many organic fluorescent sensors, the fluorescence quenching is irreversible and imposes a limitation in terms of reusability. Here we present a study of the thermal control of thin-film fluorescent sensors made from the commercial fluorescent polymer Super Yellow (SY). Thermal control of the sensor's temperature results in the desorption of the absorbed analytes, nitroaromatic explosives (2,4-DNT and DNB), and a taggant molecule (DMDNB). The amount of photoluminescence (PL) quenching and the desorption temperature of analytes provides a route to discriminate between the analytes, and additonally make the SY sensors reusable.

Overview of nano enabled sensor for analysis of explosive substances

Threats of armed conflict and terrorist attacks present difficult challenges for defense agencies around the world and are an increasing source of worry for the public and security-conscious policymakers. The environmental monitoring of residue or discarded explosives in soil, as well as the detection of ultra-low levels of explosive compounds in remote areas or under extreme conditions for anti-terrorist activities, continue to pose significant challenges. Most explosives produce very little vapors, making it difficult to detect them with common techniques for other compounds. Due to a number of factors, including the large variety of explosives substances, the enormous number of deployment methods, and the dearth of low-cost sensors with high sensitivity and selectivity makes explosive detection very complicated and expensive task. To defeat explosives-based terrorism, sensors must have high sensitivity and selectivity as well as the capacity to produce and deploy them at lower costs. Nanotechnology-based sensors have an excellent possibility of meeting all the criteria for a successful approach to explosive trace detection. The design and analytical capabilities of explosive detection systems employing nanomaterial as signal transducers are covered in this overview. The review article also discusses the importance of nano-enabled technologies for the explosive detection in security applications, gives background on the technology, and identifies other issues that need to be resolved.

A Mathematical Model for Sublimation of a Thin Film in Trace Explosive Detection Problem.

Here, we introduce an advanced mathematical model for the sublimation of thin films of explosives. The model relies on the Hertz-Knudsen-Langmuir (HKL) equation that describes the vaporization rate of an explosive and controls the mass exchange between the surface and the ambient air. The latest experimental data on sublimation and diffusion of 2,4,6-trinitrotoluene (TNT) monocrystals were factored in, as well as the data on the sublimation rate of hexogen (RDX), octogen (HMX), and picramide (TNA) traces. To advance the mathematical model we suggested previously, we took into account the structure of a substrate on which a thin explosive layer was deposited. The measurement problem of the sublimation rate and limits of an explosive arises from developing and advancing remote detection methods for explosives traces. Using mathematical modelling, we can identify a detectable quantity of a specific explosive under given conditions. We calculated the mass of the explosive in the air upon sublimation of thin explosive films from the surfaces over a wide range of the parameters in question and made conclusions regarding the application limits of the devised standoff trace explosive detection techniques.

3D plasmonic hot spots network via gold decorated deep micro-porous silicon exhibiting ultrahigh-SERS enhancement with application to explosives detection

Microporous deep (12 µm depth) silicon substrate coated with optimum Au layer is fabricated for ultrahigh SERS enhancement factor and employed for explosives trace detection. Being microporous with quasi-periodicity, short lived extended plasmons can be excited via scattering and coupled to localized ones thus providing ultrahigh local optical field, and the SERS ultrahigh enhancement is achieved. SERS activity of the substrate is checked using 4-ATP monolayer immobilized over the proposed substrate and analyzed using two different methods including peak absolute intensity and peak ratios, to find best suitable method for higher reproducibility. The obtained enhancement factor for Raman signal is found to be the order of 106–107, explained due to the existence of 3D hot-spot network and coupling between localized to extended plasmons. The coupling is verified through the Rabi splitting observed in the reflectivity dip. A 2–3 times fewer signal variability is obtained using peak ratio between highest peak intensity of Raman receptor and that of the substrate. The substrate is then employed for picric acid sensing providing the detection limits of 7.48 nM and 2.87 nM, determined based on peaks height and ratio measurements respectively. The proposed work suggests deep micro-porous silicon coated with 200 nm Au layer deposited over a large area as promising candidate for SERS and sensing of ultra-trace amount of chemicals.

Optical gas sensor based on the combination of a QD photoluminescent probe and a QD photodetector

We report on a sensor architecture for detection of hazardous gases. The proposed device is based on the integration of a solid-state quantum dot (QD) photoluminescent probe with a QD photodetector on the same substrate. The effectiveness of the approach is demonstrated by developing a compact optical sensor for trace detection of explosives in air. The proposed architecture is very simple and consists of a silicon substrate with both surfaces coated with QD films. The upper layer acts as photoluminescent probe, pumped by a blue LED. The change of photoluminescence intensity associated to the interaction between the QDs and the target analyte is measured by the QD photodetector fabricated on the opposite side of the substrate. The sensor is mounted into a small chamber provided with the LED and the front-end electronics. The device is characterized by using nitrobenzene as representative nitroaromatic compound. Extremely low concentrations (down to 0.1 ppm) can be detected by the proposed device, with a theoretical detection limit estimated to be as low as 2 ppb. Results are repeatable and no ageing effect is observed over a 70 d period. The proposed architecture may provide a promising solution for explosive detection in air as well as other sensing applications, thanks to its sensitivity, simple fabrication process, practical usability and cost effectiveness.

Benefits of Decision Support Systems in Relation to Task Difficulty in Airport Security X-Ray Screening

Automated explosive detection systems for cabin baggage screening (EDSCB) highlight areas in X-ray images of passenger bags that could contain explosive material. Several countries have implemented EDSCB so that passengers can leave personal electronic devices in their cabin baggage. This increases checkpoint efficiency, but also task difficulty for screeners. We used this case to investigate whether the benefits of decision support systems depend on task difficulty. 100 professional screeners conducted a simulated baggage screening task. They had to detect prohibited articles built into personal electronic devices that were screened either separately (low task difficulty) or inside baggage (high task difficulty). Results showed that EDSCB increased the detection of bombs built into personal electronic devices when screened separately. When electronics were left inside the baggage, operators ignored many EDSCB alarms, and many bombs were missed. Moreover, screeners missed most unalarmed explosives because they over-relied on the EDSCB’s judgment. We recommend that when EDSCB indicates that the bag might contain an explosive, baggage should always be examined further in a secondary search using explosive trace detection, manual opening of bags and other means.

Remote Raman Detection of Trace Explosives by Laser Beam Focusing and Plasmonic Spray Enhancement Methods.

Remote Raman spectroscopy is a technique that can detect and identify different target molecules through Raman vibrational modes from a remote distance. However, the current remote Raman technique is restricted by poor detection sensitivity, and it is still extremely challenging for trace explosive detection. Here, in order to achieve trace explosive detection from a remote distance, we innovatively propose two enhanced Raman spectroscopy methods by using a plasmonic spray and a laser beam focusing/Raman signal collecting instrument. In brief, a facile convex lens can converge the laser beam and collect Raman scattering signals, and a plasmonic spray can be used for surface-enhanced Raman scattering. Under the combination of the above enhancement methods, we achieve remote Raman detection of a variety of trace explosives with a concentration of ∼1 μg/cm2 from a distance of 30 m. These novel methods demonstrate a simple approach that significantly improves the capability of remote detection of trace chemicals for further applications.

Arc-Induced Nitrate Reagent Ion for Analysis of Trace Explosives on Surfaces Using Atmospheric Pressure Arc Desorption/Ionization Mass Spectrometry.

This study presents the rapid surface detection of explosives by employing atmospheric pressure arc desorption/ionization mass spectrometry (APADI-MS) using point-to-plane arc discharge. In APADI, neutral explosives readily bind to the gas-phase nitrate ion, NO3-, induced by arc discharge to form anionic adducts [M+NO3]-. This avoids the need for inorganic anionic additives such as NO3-, NO2-, Cl-, acetate, and trifluoroacetate for unique explosive ionization pathways and simplifies mass spectra. The analytical performance of APADI was thoroughly evaluated for the rapid detection of 10 explosives at levels in the range of 800 fg-1 μg. Arc-induced nitrogen oxide anions promoted the formation of characteristic adducts, such as [M+NO3]-, and improved the instrument response for all the explosives tested. APADI showed considerable sensitivity in the negative ion mode with limits of detection in the low picogram range, particularly when explosives were analyzed on a copper or aluminum foil substrate. APADI coupled with an Orbitrap mass spectrometer displayed a good linear response for the studied explosives. The linearity and intraday and interday precisions were evaluated, demonstrating the feasibility and robustness of APADI-MS for the detection of trace explosives on solid surfaces. The mechanisms of APADI for explosive ionization and desorption were examined and verified by performing density functional theory calculations.

Functionalized semiconducting carbon nanotube arrays for gas phase explosives detection

Single molecule detection systems are of considerable practical interest in sensing applications, such as disease detection or transient kinetics monitoring, where ultra-sensitive measurements are needed. Trace detection of explosives is an application where the mere presence, not necessarily the concentration, of an analyte is cause for concern. As in many other sensing applications, carbon nanotube (CNT) based devices are under study for single molecule detection systems, motivated by interest in reducing the size, cost, and power requirements of current sensing systems. Although CNT sensors have been shown to be highly sensitive to some analytes, a longstanding obstacle to the development of ultra-sensitve CNT sensors has been their lack of selectivity. Ab initio modeling of functionalized semiconducting CNT arrays suggests that they offer sensitive and selective explosives detection, capable of distinguishing explosives from common background gases, distinguishing nitroaromatic from nitramine explosives, and discriminating among distinct nitramine explosives with very similar structures.

Promising Applications of Additive-Manufactured (3D-printed) Electrochemical Sensors for Forensic Chemistry

Additive-manufacturing is one of the major pillars of the new industrial revolution and the three-dimensional (3D) printing technology has been highlighted in this scenario. Among the many areas benefited by 3D-printing, the development of electrochemical sensors has appeared in evidence in the last years. One potential application of 3D-printed electrochemical sensors is devoted to forensic chemistry, which demands for portable analytical methods that can provide on-site measurements and thus bring a relevant information in loco. In this context, this review highlights the recent contribution of 3D-printing technology on the development of electrochemical sensors with great promises for on-site analysis in “real-world” forensic scenarios. From the detection of trace explosives, gunshot residues, illicit drugs and chemical threats, to the measurement of adulterants in food and fuels, we show the wide range of applications that 3D-printed electrochemical sensors have been proposed and future demands that can be addressed by such a powerful, affordable, and accessible tool.