Thienothiophene based AIE-Active bulky materials for sensitive explosive detection

Nitro aromatics are the principal components of explosives used in acts of terrorism and within improvised explosive devices, among others. Although high sensitivity towards nitro aromatic explosives has been demonstrated, selective detection and discrimination are critical for practical applications. Fluorescence quenching of metal–organic frameworks (MOFs) is sufficiently sensitive to detect any nitro explosives, but discriminative detection with different numbers of –NO2 groups is rare. Here we report a stable fluorescent MOF, [Zn2(NDC)2(bpy)]·Gx, 1 (where NDC = 2,6-naphthalenedicarboxylic acid, bpy = 4,4′-bipyridine, and G = guest solvent molecules), whose fluorescence is quenched by trace amounts of nitro aromatics introduced from solution or in vapor phase. The steady-state and time-resolved experiments show that the quenching process is dynamic in nature and the interactions (dipole–dipole, π-stacking) between the MOF and nitro explosives play a crucial role in the discriminative detection of nitro aromatics with different numbers of –NO2 groups.

Nitroaromatic compounds are highly explosive and illegitimate substances. Over a decade, chemists have been affianced in extensive research on the selective and sensitive detection of these nitroaromatic explosives for homeland security and environmental protection. The benzodiazepine-based enaminone (BDE) receptor has been synthesized by aqueous extract of onion catalyzed three-component reaction between o-phenylenediamine, dimedone with an aldehyde. The BDE probe is well analyzed and applied to a sensor that selectively detects picric acid (PA). UV-Vis and fluorescence spectroscopy were used to investigate the photophysical responses of the receptor (BDE). From the observed results BDE found turn-off fluorescence with the addition of picric acid and the lowest limit of detection and limit of quantification was achieved about 24.6 nM and 73.8 nM. The fluorescence quantum yield was attained about 0.28. The BDE-PA adduct formation was confirmed by 1H NMR titration analysis. The Job's plot analysis was performed through 1H NMR titrations and established the binding stoichiometry ratio of the BDE-PA adduct as 1:1 ratio. Further, DFT calculations supported the observed photophysical responses of BDE-PA adduct to confirm the molecular level interactions. The receptor was effectively applied to approximate level of picric acid in real water sample analysis.

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Flexible chemiresistive sensor of polyaniline coated filter paper prepared by spraying for fast and non-contact detection of nitroaromatic explosives

Nitroaromatic compounds (NACs) that are components of explosives have become seriously endanger human health, environmental cleaning, national homeland security, etc. The development of appropriate probes for the detection of NACs with desired easy operability, rapid response, reusability and high sensitivity and selectivity advantages has remained a great challenge. Over the past few years, great efforts have been made toward the development of advanced functional materials based on aggregation-induced emission or aggregation induced emission (phosphorescence) enhancement (AIE or AIE(P)E)-active transition metal complexes(AIEgens)and their remarkable achievements in the detection of NACs due to their high quantum yield and tunable photophysical properties. In this review, a brief description of luminescent AIEgens is presented, accompanied by a study on the Ir(III), Re(I) and Pt(II)-based AIEgens as sensing materials for nitroexplosives detection. Then, the trends and challenges of AIE or AIE(P)E-active transition metal complexes for the sensitive and selective detection of nitroaromatic explosives are also discussed.

Self-assembled structures of N-alkylated bisbenzimidazolyl naphthalene in aqueous media for highly sensitive detection of picric acid

A bistable [3]rotaxane comprising [23]crown ether and a pyrene fluorophore selectively exhibited dramatic pyrene excimer emission in the presence of the dihydrogen phosphate anion due to the generation of a supramolecular assembly. The assembly was generated via hydrogen bonding between methyl triazolium moieties and the dihydrogen phosphate anion, bringing the pyrene moieties into proximity. The assembly could selectively detect picric acid over other nitroaromatics through excimer fluorescence quenching via energy transfer from the assembly and proton transfer from the picric acid. The quenching efficiency for picric acid is found to be 96%, with a limit of detection of 198 nM.

Anthracene-based fluorescent probe: Synthesis, characterization, aggregation-induced emission, mechanochromism, and sensing of nitroaromatics in aqueous media

The development of inexpensive, equipment-free, portable, and user/environmentally-friendly analytical devices that can be efficiently utilized for on-site detection of PA is still a great challenge. To address these unmet demands, we have developed a smartphone-based disposable sensing bioplatform through immobilization of chlorophyll in a cotton thread for fluorescent monitoring of picric acid (PA). The fluorescence quenching of chlorophyll upon increasing the PA concentration based on the inner filter effect was considered as the sensing strategy in the developed sensor. The fabricated thread-based microfluidic sensing bioplatform was further coupled with a compact, low cost, portable, and 3D-printed all-in-one smartphone-based analytical device (ASAD) that is able to thoroughly perform all analytical steps of PA determination in environmental samples, including sample preparation (mixing and centrifuging/separating) and analyzing steps. The satisfactory results achieved by the fabricated ASAD-based wicking sensing platform with good linearity (5.0–100.0 μM), detection limit (1.0 μM), and selectivity toward PA show its great potential to be widely exploited for easy, ultra-low-cost, sensitive, selective, and smart detection of PA, particularly at point-of-use applications, where are often far from well-equipped centralized laboratories.

Y-shaped ferrocene/non-ferrocene conjugated quinoxalines for colorimetric and fluorimetric detection of picric acid.

Volatile organic sulfur compounds (VOSCs) serve not only as biomarkers for dental diseases such as halitosis but also as a tracer for monitoring air quality. Room-temperature selective detection and superior sensitivity against VOSCs at a sub-ppm level has remained a challenging task. Here, we propose a heterostructure-based design using a MoSe2/SnO2 composite for achieving sensitive and selective detection of ethyl mercaptan at room temperature. The composite was synthesized via a facile two-step method. A composite-based device has shown detection down to 1 ppm of ethyl mercaptan over a wider range of relative humidity (40-90%). Notably, the composite has shown adsorption selectivity toward ethyl mercaptan compared to hydrogen sulfide and other reducing or oxidizing analytes. Moreover, a density functional theory (DFT) study has been performed to understand the adsorption selectivity, charge transfer, and modification in the electronic properties after molecule adsorption on the host surface. Simulations predicted the lowest negative adsorption energy for ethyl mercaptan, implying the chemisorption (-142.029 kJ mol-1) process of adsorption. The device thus-obtained has also shown a stable response even at an extreme relative humidity level of 90%. The obtained results and superior signal-to-noise ratio indicate that a MoSe2/SnO2-based sensor may be a promising candidate for highly selective and sensitive detection of ethyl mercaptan even below 1 ppm.

The relevance of the study is conditioned by the re-estimation of values in modern society and a new understanding of security issues. As a result, security has acquired a complex structure, including the security of the individual in the process of life activity, protection of natural environment (biosphere), national security and global security. The purpose of the paper is to develop practical advice for teaching of university students the mechanisms of self-government of safe behavior. The leading approach to the study is the personal-activity-based approach, which allows considering the mechanisms of self-government of safe behavior of the individual as a set of techniques and methods of self-protection of the vital interests and countering the dangers and threats. The study involves 500 teachers, 500 students who have defined the criteria for effective mechanisms of self-government of safe behavior. The main results of the study is the development of mechanisms to counter the negative information and psychological effects (cognitive, emotional, behavioral) and mechanisms of information-psychological self-protection implemented in the unconscious, the subconscious, the conscious level. The significance of the results obtained is in the fact that the developed mechanisms for countering negative information and psychological influences contribute to the effectiveness of coping behavior, achieved by specially organized activity to overcome the dangers and threats and ensure personal safety. Mechanisms of information-psychological self-protection provide protection of the individual from the internal psychological discomfort or external psychological impact, cause the formation and development of adequate information and a rough basis of life activity.

Currently, urea containing frameworks assumed to have a prominent role in the developing field of Y shapes anion detection such as TNP, TNT and their derivatives owing to their capability to act as double H-bond donors. Developing new and highly efficient sensors for detection of trace concentration of these explosives is remaining challenge. The immobilization of organic–functional struts within the pore wall of metal-organic frameworks (MOFs) is one of the new strategies to develop highly sensitive and selective receptors. Decoration of MOF skeleton with urea moiety can be helpful in effective recognizing of these specific guests for two reasons, (i) incorporation of urea strut in the framework prevents their inherent self-assembly and (ii) urea can form positive double hydrogen bond donation site which can act as a promising receptor for anionic moieties. A 3D, urea functionalized, TMU-18, has successfully synthesized as a chemosensor for selective detection by fluorescence signaling towards explosive nitroaromatics and carbonyl compounds. TMU-18 due to its special and porous structure and available functional group shows strong luminescence emission, and could be effectively used for sensitive detection of Trinitrophenol (TNP) with a 10 µM limit of detection (LOD).

Two luminescent Zn(II) metal–organic frameworks for exceptionally selective detection of picric acid

In this study, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), 2,4,6-trinitrochlorobenzene (TNCB), and 2,4,6-trinitrotoluene (TNT) were sensitively detected with the aid of alkali ions (Li+, Na+ and K+ from the corresponding nitrate salts) using surface-enhanced Raman scattering (SERS), through an extremely simple process of adding explosive compounds and alkali ions to negatively charged silver colloids. The results show that the quantitative SERS detection limit of CL-20 is 1 nM with the addition of Na+, whereas for TNCB and TNT, the corresponding detection limit can reach 0.01 nM adjusted using Na+ and K+, respectively. The possible mechanisms of the sensitive SERS detection of trace nitro-explosives (CL-20, TNCB, and TNT) with the aid of alkali ions (Li+, Na+ and K+) have been investigated by Density Functional Theory (DFT) calculations. Natural Bond Orbital (NBO) analysis of the optimized structures of CL-20, TNCB and TNT revealed that the O atoms on the nitro group of these explosives carry a relatively greater negative charge, which can be successfully coordinated with the alkali ions accompanied by an obvious energy release to form positively charged complexes. Subsequently, these complexes spontaneously approach the negatively charged silver colloid, creating more SERS active sites, thereby enhancing the Raman detection sensitivity.