Search

The detection of explosive materials, particularly nitroaromatic compounds such as 2,4,6‐trinitrotoluene (TNT), is critical for public safety and national security. Existing detection methods often require complex instrumentation, limiting their applicability for real‐time or in‐field use. Fluorescent sensors, which offer rapid and sensitive detection through fluorescence quenching, present a promising alternative. This study evaluates the performance of two pentiptycene‐based polymers, P‐1 and P‐2, in detecting explosive vapors, with a specific focus on their behavior under high‐humidity conditions. P‐2, modified with triethylene glycol groups, demonstrated significantly increased hydrophilicity compared to the commonly studied P‐1, as confirmed by contact angle measurements. Spectroscopic analysis revealed a blue shift in P‐2's UV–Vis absorption and photoluminescence spectra, indicating electronic property changes due to structural modifications. The enhanced hydrophilicity of P‐2 enabled it to maintain stable sensing performance under moist conditions, showing less than a 10% reduction in sensitivity, compared to the 20% decrease observed in P‐1. This superior moisture resistance suggests that P‐2 is a more robust and practical sensor for explosive detection in environments with variable humidity levels. [ABSTRACT FROM AUTHOR]

A highly efficient and sensitive ion mobility spectrometry (IMS) system with laser desorption sampling was applied for rapid explosive detection using different surface materials. This portable IMS detector, powered by a battery, offers mobility and is suitable for use in the field or combat zones. The laser desorption (LD) sampling of common explosives (Trinitrotoluene—TNT; Dinitrotoluenes—DNTs; Hexogene—RDX; pentaerythritol tetranitrate—PETN; plastic explosives—Compound 4 (C-4) and Semtex) on a wide range of common surface materials, such as metal, ceramic, plastic, glass, drywall, paper, wood, and textiles, was studied. Successful detection was achieved on nearly all surfaces except flammable materials (paper, wood, and textiles). The limit of detection (LOD) was determined for each explosive and specific surface, demonstrating an impressive LOD of 7 ng/mm2 for TNT. RDX, C-4, PETN, and Semtex achieved LOD values of 15 ng/mm2, while DNTs showed an LOD of approximately 50 ng/mm2. [ABSTRACT FROM AUTHOR]

Remote detection of trace explosives and hazardous chemicals has been an ongoing challenge and a critical issue in defense science, public safety, and counterterrorism. Raman spectroscopy, a form of inelastic scattering, acts as a "fingerprint" analysis method for substance identification with high confidence in the detection of chemicals based on their vibrational modes. Here, we present a portable stand-off time-gated Raman spectroscopy, which consists of a passive Q-switched pulsed laser, a designed gated ICMOS, a spectrometer, and a telescope, with an overall size of 476.5 × 321.5 × 219.3 mm and a weight of 23.2 kg, which is much more compact and portable than reported previously. To confirm the effectiveness of the designed portable time-gated Raman spectroscopy, detections at different working distances and various amounts of substances are carried out. High levels of Raman identification are acquired even for 0.1 mg at a 10-m distance. Furthermore, we simulate realistic encounters in a possible war-zone scenario by testing the system's ability to recognize urea samples on different substrates such as an aluminum plate, woodblock, cardboard, black cloth, and leaf; good characteristic recognition is shown. [ABSTRACT FROM AUTHOR]

A novel tellurium (Te) containing fluorophore, 1 and its nickel (2) and copper (3) containing metal organic complex (MOC) have been synthesized to exploit their structural and optical properties and to deploy these molecules as fluorescent probes for the selective and sensitive detection of picric acid (PA) over other commonly available nitro‐explosives. Furthermore, density functional theory (DFT) and single crystal X‐ray diffraction (SCXRD) techniques revealed the inclusion of "soft" Tellurium (Te) and "hard" Nitrogen (N), Oxygen (O) atoms in the molecular frameworks. Owing to the presence of electron rich "N" and "O" atoms along with "Te" in the molecular framework, 1 could efficiently and selectively sense PA with more than 80 % fluorescence quenching efficiency in organic medium and having detection limit of 4.60 μM. The selective detection of PA compared to other nitro‐explosives follows a multi‐mechanism based "turn‐off" sensing which includes photo‐induced electron transfer (PET), electrostatic (π‐π stacking and π‐anion/cation) interaction, intermolecular hydrogen bonding and inner filter effect (IFE). The test strip study also establishes the sensitivity of 1 for detection of PA. [ABSTRACT FROM AUTHOR]

Canines are widely used for real-time detection of explosives and have proven to be on par with instrumental methods. Canines are thought to rely largely upon detection of volatile chemical constituents of the explosives, though not necessarily the explosive itself. Hence, it is crucial to understand the odor available to them as generated by training aids. Previous studies have established that the Training Aid Delivery Device (TADD) developed by SciK9 is a reliable training aid that reduces cross-contamination and doubles as a storage device. A TADD comprises a standardized container, a synthetic membrane, a membrane holder, and a lid. In the work presented, activated charcoal strips were placed above and below the TADD membrane to determine the relative amounts of volatiles emitted by dynamite (i.e., ethylene glycol dinitrate (EGDN) and trinitroglycerin (NG)). The strips were eluted and the extracts tested using gas chromatography–mass spectrometry in negative ion chemical ionization mode. A series of t-tests at 95% confidence level were performed to determine any differences in vapor composition above and below the membranes. Nine synthetic membranes and six glass fiber membranes were tested in this study. It was expected that the relative concentration of volatiles would remain the same on both sides of the membrane; however, selective removal of nitroglycerin by some membranes was observed. Synthetic membranes with larger pore sizes showed no alteration in the vapor composition. Both synthetic and glass fiber membranes did not show a significant change in relative concentration of the other volatile compound in dynamite, i.e., EGDN. Out of all the membranes tested, three synthetic membranes and four glass fiber membranes showed selective alteration in odor availability of nitroglycerin in dynamite. For training purposes, membranes that do not alter the vapor composition should be used in the training aid. [ABSTRACT FROM AUTHOR]

The design and development of ultra‐accurate probe is of great significance to chemical sensing in complex practical scenarios. Here, a self‐accelerating naphthalimide‐based probe with fast response and high sensitivity toward hydrogen peroxide (H2O2) is designed. By coupling with the specially selected upconversion nanoparticles (UCNPs), an ultra‐accurate colorimetric‐fluorescent‐upconversion luminescence (UCL) tri‐mode platform is constructed. Owing to the promoted reaction process, this platform demonstrates rapid response (< 1 s), an ultra‐low detection limit (4.34 nM), and superb anti‐interferent ability even in presence of > 21 types of oxidants, explosives, metallic salts, daily compounds, colorful or fluorescent substances. In addition, the effectiveness of this design is further verified by a sponge‐based sensing chip loaded with the UCNPs/probe in recognizing trace H2O2 vapor from interferents with the three characteristic colors existing simultaneously. The proposed design of probe and tri‐mode visualization detection platform is expected to open up a brand‐new methodology for ultra‐accurate sensing. [ABSTRACT FROM AUTHOR]

Detection of explosives and their residues in real time is of paramount importance to homeland security and military. In real-time applications, the suspected materials may contain several chemical compounds making the detection even more challenging. We demonstrate a compact portable Raman spectroscopic tool for quantitative detection of constituent explosives in a binary mixture using machine learning. For the experiment, two samples were considered and mixed at different weight percentages:—1,3,5-trinitroperhydro-1,3,5-triazine (RDX) and ammonium nitrate (AN). Linear regression was employed to quantify the amount of RDX and AN. Regression analyses were conducted using both univariate and multivariate machine learning methods. The Raman spectra were analyzed with and without background correction. Further, various feature/variable selection strategies were explored to find out the best analysis protocol. Our analysis shows that the background correction of the spectra does not improve the accuracy. Among various feature selection techniques, multivariate analysis by considering the total spectra and features associated with only peaks as input gives better results than univariate analysis and multivariate analyses of other sub-spectra. The results demonstrate that Raman spectroscopy combined with machine learning can be used as a reliable, compact, and fast tool for the real-time investigation of explosive mixtures. [ABSTRACT FROM AUTHOR]

In the modern day, explosive detection is essential to public safety, and fluorescent small molecules have gained popularity for their quick and accurate detection. Herein, we present the design and synthesis of a series of pyrrolo[1,2-a]quinoxaline-based conjugated small organic fluorophores (PQ-Ph-OH, PQ-Ph-NMe, PQ-Ph-OMe, PQ-Ph-Me, and PQ-Ph-CN) as fluorescence-based sensors for explosive molecules. The sensor molecules were synthesized in good to excellent yields using a dehomologative functionalization strategy. They exhibited excellent photophysical characteristics, which was tunable based on the substituent on the phenyl linker at position 3. DFT studies showed that the pyrroloquinoxaline moiety could act as an on-demand electron donor or acceptor, depending on the phenyl substituent. The molecules also exhibited solid state emission due to twisted geometry around the CC single bond between the heterocyclic scaffold and the phenyl derivative. This resulted in low band intense emission for the synthesized molecules. In the presence of electron-deficient nitroaromatic explosives, all the fluorophores showed excellent fluorescence quenching. Detection limits in the range of 10−4 M were obtained for all the fluorophores. Stern-Volmer plots show high values of binding constants, indicating good interaction between the fluorophores and the explosive molecules. The mechanism of sensing was confirmed by UV-PL spectral overlap and fluorescence lifetime measurements, which suggest a static quenching based on the formation of a ground state complex. Owing to solid state emissions in some of the derivatives, the synthesized molecules were applied to paper strips for spot detection of explosive molecules.

We developed a state-of-the-art, high-sensitivity, low-stray-light standoff deep-ultraviolet (DUV) Raman spectrometer for the trace detection of resonance Raman-enhanced chemical species. As an excitation source for Raman measurements, we utilized our recently developed, second-generation, miniaturized, diode-pumped, solid-state neodymium-doped gadolinium orthovanadate (Nd:GdVO4) laser that generates quasi-continuous wave 228 nm light. This 228 nm excitation enhances the Raman intensities of vibrations of NOx groups in explosive molecules, aromatic groups in biological molecules, and various aromatic hydrocarbons. Our DUV Raman spectrograph utilizes a custom DUV f /8 Cassegrain telescope with an ∼200 mm diameter primary mirror, high-efficiency DUV transmission gratings, custom DUV mirrors, and a custom 228 nm Rayleigh rejection filter. We utilized our new standoff DUV Raman spectrometer to measure high signal-to-noise ratio spectra of ∼50 μg/cm2 drop-cast explosives: ammonium nitrate (AN), trinitrotoluene, pentaerythritol tetranitrate as well as aromatic biological molecules: lysozyme, tryptophan, tyrosine, deoxycytidine monophosphate, deoxyadenosine monophosphate at an ∼3 m distance within 10–30 s accumulation times. We roughly estimate the average ultraviolet resonance Raman (UVRR) detection limits for the relatively homogeneous drop-cast films of explosives and biological molecules to be ∼1 μg/cm2 when utilizing a continuous raster scanning that averages Raman signal over ∼1 cm2 sample area to avoid quick analyte depletion due to ultraviolet (UV) photolysis. We determined 3 m standoff UVRR detection limits for drop-cast AN films and identified factors impacting UVRR detection limits such as analyte photochemistry and analyte morphology. We found a detection limit of ∼0.5 μg/cm2 for drop-cast AN films on glass substrates when the Raman signal is averaged over ∼0.5 cm2 of sample surface using a continuous raster scan. For a step raster scan, when the probed sample area is limited to the laser spot size, the detection limit is approximately tenfold higher (∼5 μg/cm2) due to the impact of UV photochemistry. Graphical abstract This is a visual representation of the abstract. [ABSTRACT FROM AUTHOR]

In recent years, fluorescent probes based on quantum dots have become a popular tool for explosive detection. However, despite their high sensitivity, these probes still require lab-based instrumentation and procedures that are difficult to be converted into a small, low-power system. Furthermore, they are hardly applied to the detection of vapor-phase explosives, being limited to water samples. Herein, we propose two alternative ways of employing quantum dots as a sensing material to build simple devices for vapor explosive detection. First, we report on a compact optical system where a solid-state QD photoluminescent probe is successfully integrated with a QD photodetector on the same silicon chip. Therefore, a high-performance chemiresistive sensor whose electrical resistance changes proportionally to the target gas concentration is proposed. [ABSTRACT FROM AUTHOR]

Hyperbranched polymers have been widely applied in various fields because of their good solubility, high reactive end groups, and low viscosity, etc. Therefore, it is of great importance to develop new strategies to build multifunctional hyperbranched polymers with novel architectures. In this work, a C(sp3)─H activation‐based polymerization of internal alkynes and bifunctional secondary amines is successfully established, and multifunctional hyperbranched polyamines (hb‐PAs) with 100% E‐isomers and high molecular weights (Mw up to 76 500) are prepared in good yields (up to 82%). The hb‐PAs containing tetraphenylethylene moiety show unique aggregation‐enhanced emission properties and can be used for explosive detection with a low limit of detection (9.14 × 10−8 m). Notably, the hb‐PAs display high refractive indices (up to 1.7607) that can be further modulated to 1.7825 by the coordination of its peripheral ethynyl group with metallic cobalt. Moreover, the hyperbranched structure endows the hb‐PAs with much better properties than their linear counterparts, such as higher photoluminescence quantum yields and refractive indices. In addition, the hb‐PAs can be modified by a C(sp3)─H activation reaction of internal alkynes and alcohols. This work not only prepares a series of functional nitrogen‐containing hyperbranched polymers but also promotes the application of C(sp3)─H activation in polymer chemistry. [ABSTRACT FROM AUTHOR]

Thin films of two poly(dendrimer)s were studied for the detection of trace quantities of nitro-based taggants and explosives. The poly(dendrimer) structures consist of side chain-conjugated triphenylamine-based dendritic chromophores attached to a non-conjugated polymer backbone. The poly(dendrimer)s differ in terms of the conjugation length, steric bulk and surface groups of the chromophores and we investigated the effects of these differences on sensing performance. We found that the addition of first-generation biphenyl-based dendrons to the chromophores of one of the polymers, P2 , resulted in greater photoluminescence quenching, sensitivity and recovery to pulses of the vapours of the nitroaliphatic taggant 2,3-dimethyl-2,3-dinitrobutane (DMNB) and the nitroaromatic analyte 2,4-dinitrotoluene (2,4-DNT) compared with the other polymer, P1. We employed neutron reflectometry to characterise the vapour uptake of both poly(dendrimer)s and a structurally similar triphenylamine-based dendrimer D1 for comparison. The results show that the P2 has a mass density of 0.91 ± 0.01 v. 1.01 ± 0.01 g cm−3 for both P1 and D1 and can absorb at least twice the amount of 2,4-DNT. These results show how increasing the dendritic character of the poly(dendrimer) architecture provides a route for optimising vapour uptake and improving sensing performance in the solid state. Thin films of two poly(dendrimer)s differing in conjugation length, steric bulk and surface groups were studied for the detection of trace quantities of nitro-based taggant and explosive vapours. Addition of first-generation biphenyl-based dendrons led to a decrease in mass density, an increase in analyte sorption and improved detection. (Image credit: Paul L. Burn.) CH23131_TOC.jpg [ABSTRACT FROM AUTHOR]

Abstract We study the electrical and morphological properties of random arrays of Ge nanowires (NW) deposited on sapphire substrates. NW-based devices were fabricated with the aim of developing chemiresistive-type sensors for the detection of explosive vapours. We present the results obtained on pristine and annealed NWs and, focusing on the different phenomenology observed, we discuss the critical role played by NW–NW junctions on the electrical conduction and sensing performances. A mechanism is proposed to explain the high efficiency of the annealed arrays of NWs in detecting 2,4,6 trinitrotoluene vapours. This study shows the promising potential of Ge NW-based sensors in the field of civil security.

Explosive detection is crucial for public safety and confidence. Among various solutions for this purpose, hyperspectral imaging differs from its alternatives with its detection capability from standoff distances. However, the state-of-the-art for such a technology is still significantly missing a complete technical and experimental framework for surveillance applications. In this article, an end-to-end technical framework, which involves capturing, preprocessing, reflectance conversion, target detection, and performance evaluation stages, is proposed to reveal the potential of a ground-based hyperspectral image (HSI) surveillance system for the detection of explosive traces. The proposed framework utilizes a short-wave infrared region (0.9–1.7 μm), which covers the distinctive absorption characteristics of different explosives. Three classes of detection methods, namely index, signature, and learning-based methods are adapted to the proposed surveillance system. Their performances are compared over various experiments, which are specifically designed for granular and sprayed residues, fingerprint residues, and explosive traces on vehicles. The experiments reveal that the best method in terms of precision and recall performances is hybrid structure detector, which effectively combines signature-based detection with unmixing. While deep-learning-based methods have also achieved satisfactory precision values, their low recall values for the moment have comparatively limited their usage for the high-risk cases. Although one of the main reasons for the current performances of deep-learning methods is less data for learning, these performances for HSIs can be increased with more data in the future as in other image applications.

The rapid detection of buried landmines has become a crucial concern of global security owing to the advancement in terrorist attacks. Indeed, the development of smart materials for the rapid detection of explosives especially nitro‐explosives is the need of time. However, the sensitivity and selectivity of materials for the detection of nitro‐explosives are major hurdles due to their low vapour pressure at room temperature. Albeit, it could be resolved by the use of advanced functional nanomaterials bearing high surface area and excellent optoelectronic properties. In this context, the water‐soluble MoS2 quantum dots (QDs) are synthesized by an ultrafast eco‐friendly hot injection method and potentially used for the detection of nitro‐explosives. The detection of picric acid (PA), 2,4,6‐Trinitrotoluene (TNT) and various other nitroaromatic compounds is performed by fluorescent probe technique. Notably, MoS2 QDs have effectively detected picric acid and TNT exhibiting detection limits of 5.13 ppm and 43.93 ppm respectively in water via a photoinduced electron transfer mechanism. Real‐time analysis of picric acid employing a paper strip of MoS2 QD as a fluorescent probe clearly demonstrates MoS2 QDs′ potential for practical usage in explosive detection. This work is patented: Application No. 202121000715 (applied). [ABSTRACT FROM AUTHOR]

Precisely optimizing the morphology of functional hybrid polymeric systems is crucial to improve its photophysical property and further extend their optoelectronic applications. The physic-chemical property of polymeric matrix in electrospinning (ES) processing is a key factor to dominate the condensed structure of these hybrid microstructures and further improve its functionality. Herein, we set a flexible poly(ethylene oxide) (PEO) as the matrix to obtain a series of polydiarylfluorenes (including PHDPF, PODPF and PNDPF) electrospun hybrid microfibers with a robust deep-blue emission. Significantly different from the rough morphology of their poly(N-vinylcarbazole) (PVK) ES hybrid fibers, polydiarylfluorenes/PEO ES fibers showed a smooth morphology and small size with a diameter of 1∼2 µm. Besides, there is a relatively weak phase separation under rapid solvent evaporation during the ES processing, associated with the hydrogen-bonded-assisted network of PEO in ES fibers. These relative "homogeneous" ES fibers present efficient deep-blue emission (PLQY>50%), due to weak interchain aggregation. More interestingly, low fraction of planar (β) conformation appears in the uniform PODPF/PEO ES fibers, induced by the external traction force in ES processing. Meanwhile, PNDPF/PEO ES fibers present a highest sensitivity than those of other ES fibers, associated with the smallest diameter and large surface area. Finally, compared to PODPF/PVK fibers and PODPF/PEO amorphous ES fibers, PODPF/PEO ES fibers obtained from DCE solution exhibit an excellent quenching behavior toward a saturated DNT vapor, mainly due to the synergistic effect of small size, weak separation, β-conformation formation and high deep-blue emission efficiency. [ABSTRACT FROM AUTHOR]

Self-assembly of π-conjugated compounds into supramolecular polymers has received considerable attention because of their intrinsic scientific interests and technological applications. As compared to π-conjugated rods, discotics, and macrocycles, propeller-shaped π-conjugated molecules have been less exploited to form long-range-ordered supramolecular polymers. Herein a novel type of supramolecular polymers has been constructed on the basis of propeller-shaped triphenylamine cyanostilbenes. The designed compound adopts nucleation—elongation cooperative mechanism for the supramolecular polymerization process, because of the participation of three-fold hydrogen bonds between the neighbouring monomers. The supramolecular polymeric state displays amplified chirality and enhanced emission than those in the monomeric state. The resulting supramolecular polymers exhibit severe emission quenching upon addition of 2,6-dinitrotoluene, ascribed to photoinduced electron transfer from the triphenylamine cyanostilbenes to the explosive analyte. The current study proves the feasibility to supramolecular polymerize propeller-like π-conjugated molecules, serving as a promising type of explosive sensor owing to their guest encapsulation and signal amplification capabilities. [ABSTRACT FROM AUTHOR]

[Display omitted] • Thienothiophene (TT) based AIE probes for explosives; trinitrotoluene (TNT), dinitrotoluene (DNT) and trinitrophenol (TNP). • 2.9 x 104 of maximum Stern-Volmer constant. • 90% of TNP quenching sensitivity. • Visual detection on the absorbent paper. Sensors for selective and sensitive detection of nitroaromatic (NAC) explosives are of current interest for both national security and environmental protection. In this work, three thienothiophene based AIE active materials (TPE2-TT, TPE3-TT and TPE3-TPA-TT), possessing tetraphenylethylene and triphenylamine units, were designed and synthesized as chemosensors for sensitively detecting 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (DNT) and trinitrophenol (TNP) explosives. Among the AIEgens, TPE3-TT demonstrated a maximum Stern-Volmer constant (K sv) reaching to 2.9 x 104 M−1 by quenching response toward TNP. They exhibited vivid visual quenching on absorbent papers. Moreover, probe-explosive complex interactions and their mechanisms were investigated using density functional theory (DFT). Their remarkable properties indicated that TT based AIEgens are promising probes for sensitively detecting the explosives, which provided a new source of potential leading to new designs for detection of explosives. [ABSTRACT FROM AUTHOR]

Abstract The precise regulation of interactions provided by aggregation‐induced emission (AIE) probes is of considerable significance for improving the sensing performance in the field of on‐site detection. Here, a highly sensitive perchlorate detection probe was designed by precisely modulating the van der Waals interactions by adjusting the length of the alkyl chain. The optimized AIE probe demonstrated superior perchlorate detection performance owing to its strong van der Waals interactions with perchlorate, including a low detection limit (53.81 nM), rapid response (

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. [ABSTRACT FROM AUTHOR]

The use of explosive materials by terrorists for mass killing, creating chaos and producing threat to people initiated the research for developing the techniques and equipments which can detect explosives. Recently a vehicle borne suicide bomber attacked CRPF convoy at Lethpora in Pulwama district in India on 14th February 2019, which killed 40 CRPF personnel. From decades, real-time detection and identification of traces of explosives at a standoff distance has been an ongoing challenge and critical problems in public safety, defense and counter terrorism. A number of methods has been successfully developed and used commercially and by defense which involves fluorescence quenching sensor, colorimetric kits and ion mobility spectrometers. While several methods are under investigation for explosive trace detection. The ideal trace detection of explosives is which can detect traces from a standoff distance and ensures personnel safety. This paper provides study of explosive detection methods, standoff spectroscopy based methods, LIBS and compares the existing methods for trace detection. Also the paper provides review of world's smallest drone made by Israel (Spectrodrone) which can sniff explosives and drugs from 2.8 km. [ABSTRACT FROM AUTHOR]

We study the electrical and morphological properties of random arrays of Ge nanowires (NW) deposited on sapphire substrates. NW-based devices were fabricated with the aim of developing chemiresistive-type sensors for the detection of explosive vapours. We present the results obtained on pristine and annealed NWs and, focusing on the different phenomenology observed, we discuss the critical role played by NW–NW junctions on the electrical conduction and sensing performances. A mechanism is proposed to explain the high efficiency of the annealed arrays of NWs in detecting 2,4,6 trinitrotoluene vapours. This study shows the promising potential of Ge NW-based sensors in the field of civil security. [ABSTRACT FROM AUTHOR]

Poly(4-trimethylsilyl diphenyl acetylene) (PTMSDPA) has strong fluorescence emission, but its application is limited by the effect of aggregation-caused quenching (ACQ). Copolymerization is a commonly used method to adjust the properties of polymers. Through the copolymerization of 4-trimethylsilyl diphenyl acetylene and 1-trimethylsilyl-1-propyne (TMSP), we successfully realized the conversion of PTMSDPA from ACQ to aggregation-induced emission (AIE) and aggregation-induced emission enhancement (AEE). By controlling the monomer feeding ratio and with the increase of the content of TMSDPA inserted into the copolymer, the emission peak was red-shifted, and a series of copolymers of poly(TMSDPA-co-TMSP) that emit blue–purple to orange–red light was obtained, and the feasibility of the application in explosive detection was verified. With picric acid (PA) as a model explosive, a super-quenching process has been observed, and the quenching constant (KSV) calculated from the Stern–Volmer equation is 24,000 M−1, which means that the polymer is potentially used for explosive detection. [ABSTRACT FROM AUTHOR]

In response to the growing concerns about the unauthorized use of advanced secondary explosives such as TKX-50 against non-combatant targets, there is an urgent need for effective detection methods or techniques to ensure efficient security screening, homeland security, and public safety. Herein, a new polymeric receptor (IV) derived from functionalized tetraphenylethylene moiety (TPE) and 1,3,5-tris(4-aminophenyl)benzene (TAPB)  moieties for the efficient detection of TKX-50 through a 'switch ON' luminescence response upon specific binding to the explosive, is reported. The observed 'luminescence ON' response is rationalized based on a charge transfer complex formation between TKX-50 and the polymeric receptor IV (K a = 1.7 × 10 4 m -1 ). This is validated by the steady and excited-state luminescence studies, along with detailed computational studies. The authors' presumptions are further validated with adequate control studies using an appropriate monomeric derivative (III) of TPE. Moreover, this 'luminescence ON' response can be integrated into a smart and user-friendly Internet of Things (IoT)-based prototype device. This device can effectively convert optical responses into digital output to develop an optical device for real-time detection of TKX-50 in solution. This lightweight, portable device is ideally suited for remote surveillance and monitoring of TKX-50; such examples are rare in contemporary literature., (© 2024 Wiley‐VCH GmbH.)

Detection of explosives is vital for protection and criminal investigations, and developing novel explosives’ sensors stands at the forefront of the analytical and forensic chemistry endeavors. Due to the presence of terminal nitro groups that can be electrochemically reduced, nitroaromatic compounds (NACs) have been an analytical target for explosives’ electrochemical sensors. Various electrode materials have been used to detect NACs in solution, including glassy carbon electrodes (GCE), platinum (Pt), and gold (Au) electrodes, by tracking the reversible oxidation/reduction properties of the NACs on these electrodes. Here, we show that the reduction of dinitrobenzene (DNB) on oxide-free silicon (Si–H) electrodes is irreversible with two reduction peaks that disappear within the successive voltammetric scanning. AFM imaging showed the formation of a polymeric film whose thickness scales up with the DNB concentration. This suggest that Si–H surfaces can serve as DNB sensors and possibly other explosive substances. Cyclic voltammetry (CV) measurements showed that the limit of detection (LoD) on Si–H is one order of magnitude lower than that obtained on GCE. In addition, EIS measurements showed that the LoD of DNB on Si–H is two orders of magnitude lower than the CV method. The fact that a Si–H surface can be used to track the presence of DNB makes it a suitable surface to be implemented as a sensing platform. To translate this concept into a sensor, however, it would require engineering and fabrication prospect to be compatible with the current semiconductor technologies.

Two aggregation induced emission (AIE)‐active poly(acrylates) bearing triphenylvinyl‐functionalized phenylcarbazole and triphenylamine pendants, respectively, were synthesized. Their fluorescence response to nitroaromatics and electrofluorochromic (EFC) properties were studied, whereby both the presence of nitroaromatics and applied voltages led to fluorescence quenching. In a very first attempt to perform EFC detection of nitroaromatics, it was surprisingly found that after initial fluorescence quenching, the presence of nitroaromatics unexpectedly turned on fluorescence at high applied voltages (>+1.0 V), demonstrating a promising approach for the EFC detection of nitroaromatic explosives. [ABSTRACT FROM AUTHOR]

Explosives pose significant threats to global safety and cause widespread environmental concerns, thus the development of rapid and reliable detection methods for explosives is highly important. In recent years, metal nanoclusters (MNCs) have garnered considerable attention due to their ultrasmall size, well-defined structure, distinct fluorescent properties and tailorable surface chemistry, making them promising for the design of robust fluorescent explosive sensors. This review first summarizes the sensing mechanisms based on MNCs for explosive detection, and then provides an overview of sensing strategies and detection performance utilizing three primary types of MNCs (gold, silver, and copper NCs). Finally, current challenges and future development prospects of MNC-based sensors for explosive detection are discussed. [Display omitted] • The fluorescent detection mechanisms of MNC-based explosive sensors are reviewed. • The sensing strategies, and performance utilizing Au, Ag, and CuNCs are summarized. • Current challenges and future prospects of MNCs in explosive detection are discussed. [ABSTRACT FROM AUTHOR]

The sensitive and selective detection of nitroaromatic explosives is of great significance to national security and human health. Herein, the novel linear polymer l-PAnTPE and cross-linked polymer PAnTPE nanoparticles based on anthracene and tetraphenylethene groups were designed and successfully synthesized via Suzuki-miniemulsion polymerization. The particle sizes of the polymers are around 73 nm, making them well dispersible in water. The cross-linked polymer PAnTPE exhibits porous structure, which is beneficial for the diffusion/adsorption of analytes. The fluorescence sensing towards nitroaromatics was performed in the aqueous phase, and l-PAnTPE and PAnTPE nanoparticles showed different quenching degree towards different nitroaromatics. Among them, the quenching constant KSV values of l-PAnTPE and PAnTPE towards 2,4,6-trinitrophenol (TNP) reach 1.8 × 104 M−1 and 4.0 × 104 M−1, respectively, which are 1–2 orders of magnitude higher than other nitroaromatic explosives, thus demonstrating the high sensitivity and selectivity of TNP detection in the aqueous phase. The sensing mechanism was further discussed to clarify this phenomenon by analyzing UV–Vis absorption, excitation, fluorescence spectra, cyclic voltammograms and fluorescence decay measurements. In addition, the paper strips tests exhibit that l-PAnTPE and PAnTPE have great potential in the application of fast, low-cost and on-site nitroaromatics detection. [ABSTRACT FROM AUTHOR]

Although it is well-known that nitroaromatic compounds quench the fluorescence of different conjugated polymers and form colored Meisenheimer complexes with proper nucleophiles, the potential of paper as a substrate for those macromolecules can be further developed. This work undertakes this task, impregnating paper strips with a fluorene-phenylene copolymer with quaternary ammonium groups, a bisfluorene-based cationic polyelectrolyte, and poly(2-(dimethylamino)ethyl methacrylate) (polyDMAEMA). Cationic groups make the aforementioned polyfluorenes attachable to paper, whose surface possesses a slightly negative charge and avoid interference from cationic quenchers. While conjugated polymers had their fluorescence quenched with nitroaromatic vapors in a non-selective way, polyDMAEMA-coated papers had a visual response that was selective to 2,4,6-trinitrotoluene (TNT), and that could be easily identified, and even quantified, under natural light. Far from implying that polyfluorenes should be ruled out, it must be taken into account that TNT-filled mines emit vapors from 2,4-dinitrotoluene (DNT) and dinitrobenzene isomers, which are more volatile than TNT itself. Atmospheres with only 790 ppbv TNT or 277 ppbv DNT were enough to trigger a distinguishable response, although the requirement for certain exposure times is an important limitation. [ABSTRACT FROM AUTHOR]

Copyright of Engineer Military Bulletin / Muszaki Katonai Közlöny is the property of National University of Public Service and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The development of reliable methods for the rapid and selective detection of nitro-explosive were vital concern for national security due to the increasing use of explosive materials in terrorism, military operation safety, industrial and environmental safety control. Here a novel cross-linked supramolecular polymer network (SPN5) was efficiently constructed by pillar[5]arene-based host–guest interactions, which can be used for nitro explosives o-DNB and p-DNB detection. The limits of detection (LODs) of SPN5 for o-DNB and p-DNB were determined as 7.90 × 10−7 M and 4.40 × 10−7 M, respectively. Moreover, the detection of o-DNB and p-DNB was also realized in a thin film consisting of the SPN5. This work provided a novel strategy for efficient detection of explosives. [ABSTRACT FROM AUTHOR]

Detection of explosives is vital for protection and criminal investigations, and developing novel explosives' sensors stands at the forefront of the analytical and forensic chemistry endeavors. Due to the presence of terminal nitro groups that can be electrochemically reduced, nitroaromatic compounds (NACs) have been an analytical target for explosives' electrochemical sensors. Various electrode materials have been used to detect NACs in solution, including glassy carbon electrodes (GCE), platinum (Pt), and gold (Au) electrodes, by tracking the reversible oxidation/reduction properties of the NACs on these electrodes. Here, we show that the reduction of dinitrobenzene (DNB) on oxide-free silicon (Si–H) electrodes is irreversible with two reduction peaks that disappear within the successive voltammetric scanning. AFM imaging showed the formation of a polymeric film whose thickness scales up with the DNB concentration. This suggest that Si–H surfaces can serve as DNB sensors and possibly other explosive substances. Cyclic voltammetry (CV) measurements showed that the limit of detection (LoD) on Si–H is one order of magnitude lower than that obtained on GCE. In addition, EIS measurements showed that the LoD of DNB on Si–H is two orders of magnitude lower than the CV method. The fact that a Si–H surface can be used to track the presence of DNB makes it a suitable surface to be implemented as a sensing platform. To translate this concept into a sensor, however, it would require engineering and fabrication prospect to be compatible with the current semiconductor technologies. [ABSTRACT FROM AUTHOR]

To address hidden explosive identification in luggage, a luggage detection system was designed based on PGNAA technology in this study. A multidetector structure was designed, and hardware modules were optimized based on a Signal-to-Noise-Ratio optimization method. Furthermore, a Weighted Spectra Library (WSL) method was proposed for spectral analysis. Combining the optimized device with the WSL method, the feasibility of the device for explosive detection was assessed both in MCNP simulation and by experimental measurement. Finally, the measurement performance of the device was further investigated, the minimum detectable mass of explosive was 200 g, and the minimum detection time was 60 s at 1000 g explosive based on the present system. [ABSTRACT FROM AUTHOR]

Both TATP and HMTD could be phlegmatized by coprecipitation with active charcoal resulting in mixtures with a nominal content of 40 wt‐% (d40‐TATP) and 10 wt‐% (d10‐HMTD), respectively. In terms of impact and friction sensitivity for both peroxides a content of 40 wt‐% resulted in >30 Nm impact sensitivity and >360 N friction sensitivity. Both phlegmatized peroxides passed the Koenen Tube and Thermal Stability Test according to the UN recommendation on the transport of dangerous goods test manual. Investigations with a process mass spectrometer indicate that d40‐TATP can produce a saturated TATP headspace at least in the same time as the same amount of pure TATP. Measurements with the transpiration method demonstrated that the vapor pressure psat at 298.15 K of d40‐TATP (2.3 Pa) and d32.7‐TATP (0.9 Pa) is lower than that of pure TATP (6.7 Pa). Headspace SPME‐GC/MS measurements revealed that the active charcoal does not contribute to the vapor profile of the training aid. Both d40‐TATP and d10‐HMTD were tested as training aids for explosive detection dog teams (EDD). In both differentiation track and realistic environment scenarios a detection rate of 100 % could be achieved by German Federal Police EDD with a false positive rate of solely 3 %. [ABSTRACT FROM AUTHOR]

This work has prepared polymeric self‐assembled monolayer (SAM) sensors for the detection of trace volatile nitroaromatic compound (NAC) explosives by fluorescence quenching. A typical aggregation‐induced emission (AIE) luminogen 1,1,2,2‐tetraphenylethene (TPE) polymerizes into PTPE to increase the fluorescence intensity in the SAMs, and the phosphoric acid acts as the anchor group to form stable covalent bonds with the Al2O3 substrate. This design takes advantage of the high sensitivity and good stability of SAMs, and high fluorescence intensity, and "wire effect" of the conjugated polymers. The polymeric SAM sensors are prepared on the Al2O3 silicon wafer and testing paper. Both of them show good response speed, reversibility, selectivity, and sensitivity. The detection limits down to 0.07, 0.35, and 4.11 ppm for TNT, DNB, and NB, respectively, are achieved on the inorganic testing paper. Furthermore, due to the higher fluorescence intensity by interlacing and overlapping of fibers, the detection of the paper can be distinguished by naked eyes even with a low‐power handheld UV lamp, which provides an experimental basis for the development of cheap and easy trace NAC explosive sensors. [ABSTRACT FROM AUTHOR]

The sensitive and selective detection of nitroaromatic explosives is of great significance to national security and human health. Herein, the novel linear polymer l-PAnTPE and cross-linked polymer PAnTPE nanoparticles based on anthracene and tetraphenylethene groups were designed and successfully synthesized via Suzuki-miniemulsion polymerization. The particle sizes of the polymers are around 73 nm, making them well dispersible in water. The cross-linked polymer PAnTPE exhibits porous structure, which is beneficial for the diffusion/adsorption of analytes. The fluorescence sensing towards nitroaromatics was performed in the aqueous phase, and l-PAnTPE and PAnTPE nanoparticles showed different quenching degree towards different nitroaromatics. Among them, the quenching constant KSV values of l-PAnTPE and PAnTPE towards 2,4,6-trinitrophenol (TNP) reach 1.8 × 104 M−1 and 4.0 × 104 M−1, respectively, which are 1–2 orders of magnitude higher than other nitroaromatic explosives, thus demonstrating the high sensitivity and selectivity of TNP detection in the aqueous phase. The sensing mechanism was further discussed to clarify this phenomenon by analyzing UV–Vis absorption, excitation, fluorescence spectra, cyclic voltammograms and fluorescence decay measurements. In addition, the paper strips tests exhibit that l-PAnTPE and PAnTPE have great potential in the application of fast, low-cost and on-site nitroaromatics detection.

Exposing different facets on metal-organic frameworks (MOFs) is highly desirable to enhance the performance for various applications, however, exploiting a concise and effective approach to achieve facet-controlled synthesis of MOFs remains challenging. Here, by modulating the ratio of metal precursors to ligands, the facet-engineered iron-based MOFs (Fe-MOFs) exhibits enhanced catalytic activity for Fenton reaction are explored, and the mechanism of facet-dependent performance is revealed in detail. Fully exposed (101) and (100) facets on spindle-shaped Fe-MOFs enable rapid oxidation of colorless o-phenylenediamine (OPD) to colored products, thereby establishing a dual-mode platform for the detection of hydrogen peroxide (H 2 O 2 ) and triacetone triperoxide (TATP). Thus, a detection limit as low as 2.06 nm is achieved, and robust selectivity against a wide range of common substances (>16 types) is obtained, which is further improved by incorporating a deep learning architecture with an SE-VGG16 network model, enabling precise differentiation of oxidizing agents from captured images. The present strategy is expected will shine light on both the rational synthesis of nanomaterials with modulated morphologies and the exploitation of high-performance trace chemical sensors., (© 2024 Wiley‐VCH GmbH.)

This paper presents a hybrid pattern recognition with temperature compensation (HPR-TC) used within an E-Nose system. HPR-TC with E-nose has the novelty, amongst MEMS sensor platforms, of having two modes of operation i.e., rapid mode of detection to be used in time-critical conditions and comprehensive analysis mode for improved detection accuracy. Two modes of operations in HPR-TC are possible because of the implementation of hybrid PR featuring a combination of two different data analysis techniques for explosive sensing. The first part of the hybrid PR is the binary PR based on threshold-based detection and the second one is the analog PR based on PCA and K-mean. The E-Nose system with proposed HPR-TC is validated with two different highly sensitive MEMS sensor types, i.e., SU8 and Si3Nx piezo-resistive cantilever. These MEMS sensors are coated with surface receptors, 4-MBA, 6-MNA and 4-ATP, to improve the selectivity. The E-Nose system can detect explosive compounds such as TNT, RDX, and PETN, in a controlled environment at a concentration as low as 16ppb of TNT, 56ppb of RDX and 134ppb of PETN. Furthermore, measurements show that E-Nose with temperature compensated binary PR can detect the explosives with a detection accuracy higher than 74% as true positives and higher than 79% as true negatives in a short time, within initial 17 seconds of the experiment. However, the temperature compensated analog PR gives a detailed classification of explosives with a higher detection accuracy of 80% as true positives and 86% as true negatives after approximately 95 seconds. [ABSTRACT FROM AUTHOR]

The efficiency and effectiveness of airport security can be improved through fast and high-fidelity detection of concealed threat objects. If detected objects can be accurately characterized, the number of false alarms will be reduced, whereas terrorist threats can be more quickly noticed and apprehended. This article aims to accurately characterize the physical properties of weak dielectric objects (such as explosive threats) covering a conductive plane (such as the human body) using a single-frequency millimeter-wave (mm-wave) radar system with a Fresnel aperture. While the conventional synthetic aperture radar (SAR) method requires data over a broad bandwidth, our proposed method works even at a single frequency and is particularly suitable for focused-beam CW mm-wave sensing systems. This method is validated with experimental data. [ABSTRACT FROM AUTHOR]

Azide-alkyne click polymerization has become a powerful tool for polymer synthesis. However, the click polymerization between internal alkynes and azides is rarely utilized to prepare functional polymers. In this work, the polymerization reactions of activated internal alkyne monomers of tris(2-butynoate)s (1) with tetraphenylethene-containing diazides (2) were performed in dimethylformamide (DMF) under simple heating, affording four hyperbranched poly(methyltriazolylcarboxylate)s (hb-PMTCs) with high molecular weights (Mw up to 2.4 × 104) and regioregularities (up to 83.9%) in good yields. The hb-PMTCs are soluble in common organic solvents, and thermally stable with 5% weight loss temperatures up to 400 °C. They are non-emissive in dilute solution, but become highly emissive in aggregated state, exhibiting aggregation-induced emission characteristics. The polymers can generate fluorescent photopatterns with high resolution, and can work as fluorescent sensors to detect nitroaromatic explosive with high sensitivity. [ABSTRACT FROM AUTHOR]

Functionalized gravimetric sensors are a promising path to small, versatile, real-time vapor sensors for volatile organic compounds. Many of these compounds can be dangerous to human health, but their nonreactive nature makes them notoriously difficult to sense. Unlike bulk acoustic resonators, chemiresistive devices have been investigated extensively and many researchers have used innovative synthesis strategies to functionalize these devices. In this work, we demonstrate how modifying a particular sensitizer for use with a bulk acoustic resonator significantly improves the sensitivity of the device (5 ppm vs. 1.11 ppm). Additionally, readout circuitry is described to avoid some problems that typically plague gravimetric sensors while simplifying the overall system. These strategies create a playbook for simple, fast, and sensitive systems for sensing volatile organic compounds, while also demonstrating the lowest limit of detection for cyclohexanone outside of gas chromatography/mass spectrometery in the literature. [2020-0053] [ABSTRACT FROM AUTHOR]