A single molecular fluorescent probe for selective and sensitive detection of nitroaromatic explosives: A new strategy for the mask-free discrimination of TNT and TNP within same sample

Paper and nylon based optical tongues with poly(p-phenyleneethynylene)-fluorophores efficiently discriminate nitroarene-based explosives and pollutants

Discrimination of nitroarenes with hydrophobic dyes in a polar (H2O) environment is difficult but possible via a lab-on-chip, with polymeric dyes immobilized on paper or nylon membranes. Here arrays of 12 hydrophobic poly(p-phenyleneethynylene)s (PPEs), are assembled into a chemical tongue to detect/discriminate nitroarenes in water. The changes in fluorescence image of the PPEs when interacting with solutions of the nitroarenes were recorded and converted into color difference maps, followed by cluster analysis methods. The variable selection method for both paper and nylon devices selects a handful of PPEs at different pH-values that discriminate nitroaromatics reliably. The paper-based chemical tongue could accurately discriminate all studied nitroarenes whereas the nylon-based devices represented distinguishable optical signature for picric acid and 2,4,6-trinitrotoluene (TNT) with high accuracy.

Metal-organic frame material encapsulated Rhodamine 6G: A highly sensitive fluorescence sensing platform for the detection of picric acid contaminants in water

As a water pollutant with excellent solubility, 2,4,6-trinitrophenol (also known as picric acid, PA) poses a potential threat to the natural environment and human health, so it is crucial important to detect PA in water. In this study, a novel composite material (MIL-53(Al)@R6G) was successfully synthesized by encapsulating Rhodamine 6G into a metal-organic frame material, which was used for fluorescence detection of picric acid (PA) in water. The composite exhibits bright yellow fluorescence emission with a fluorescence quantum yield of 58.23 %. In the process of PA detection, the composite has excellent selectivity and anti-interference performance, and PA can significantly quench the fluorescence intensity of MIL-53(Al)@R6G. MIL-53(Al)@R6G has the advantages of fast detection time (20 s), wide linear range (1-100 µM) and low detection limit (4.8 nM). In addition, MIL-53(Al)@R6G has demonstrated its potential for the detection of PA in environmental water samples with satisfactory results.

Highly sensitive fluorescent triarylimidazole derivatives for sensing of 2,4,6-trinitrophenol in aqueous solution and its application for actual environment detection

Two highly sensitive fluorescent triarylimidazole derivatives were synthesized by modifying imidazole with coumarin and large conjugate rigid plane structure. XM-F and XM-L emitted bright yellow-green fluorescent light. Their intense conjugation system generated strong π-π electrostatic interactions with TNP, accompanied by the formation of hydrogen bonds to achieve rapid detection of TNP within 25 s. The detection limits were as low as 0.049 μM and 0.071 μM, respectively. Probes had been successfully applied to rapid detection of TNP in real water samples and manufactured into portable fluorescent test strips. In view of excellent performance of XM-F, it was used to achieve real-time, portable, on-site quantitative detection of TNP by a colorimeter and a smartphone platform. In addition, XM-F also successfully processed into probe-coated TLC plates for efficient detection of fingerprints contaminated with TNP.

To Quench or Not: Extending a β-Carboline Fluorophore for TNT Detection in Aqueous Media via Simultaneous ESPT Destabilization and AIE

Molecules relying on the excited-state intramolecular proton transfer/excited-state proton transfer (ESIPT/ESPT) mechanism are widely used in material science. In the current work, a known β-carboline-based probe TrySy was used to selectively detect explosive trinitrotoluene (TNT) in water. Compared to conventional TNT sensing, which relies mainly on the quenching of the fluorescence signal, TrySy could perform nanomolar detection of TNT via ESPT destabilization and AIE, with a significant fluorescence output. The mechanism followed was validated by computational and experimental results.

Polyethyleneimine-capped copper nanoclusters for detection and discrimination of 2,4,6-trinitrotoluene and 2,4,6-trinitrophenol

The detection and discrimination of 2,4,6-trinitrotoluene (TNT) and 2,4,6-trinitrophenol (TNP) from analogues are of great importance to global security and are full of challenges in the field of trace sensing. Here, benefitting from the strong electrophilicity of TNT, a sensing strategy is established by synthesizing polyethyleneimine capped copper nanoclusters (PEI-Cu NCs) with abundant -NH₂ groups. By carefully controlling the size and structure of PEI-Cu NCs, Förster resonance energy transfer (FRET) from PEI-Cu NCs to the Meisenheimer complex occurs resulting from their spectral overlap when detecting TNT, while, due to the energy level match of TNP with PEI-Cu NCs, as well as the strong affinity between its -OH and -NH₂ in PEI-Cu NCs, photo-induced electron transfer (PET) is feasibly expected. As a result, TNT and TNP could be detected from 26 types of analogues and cations with a limit of detection (LOD) of 26.57 and 12.82 nM, respectively. Besides, owing to the brown color of the Meisenheimer complex, the discrimination of TNT and TNP could be additionally realized by colorimetric detection. We expect that the proposed methodology would not only shine light on the detection and discrimination of TNT and TNP that mitigate against public security concerns, but also pave a way for the deep understanding of FRET and PET related fluorescence quenching mechanisms from the aspect of controllable sensing material design and synthesis.

Further Develop 1,3,4-Thiadiazole Based Probe to Effectively Detect 2,4,6-Trinitrophenol with the Help of DFT Calculations

Four fluorimetric probes had been developed to rapidly detect 2,4,6-trinitrophenol (TNP). They were designed and synthesized on the basis of 1,3,4-thiadiazole framework combining calculation with experiment. Among them, SK-1 displayed strong blue emission with fluorescence quantum yield as high as 63.6% in solution. Further evaluation demonstrated that SK-1 displays good selectivity and high sensitivity for rapid and visual detection of TNP. It brought significant changes in both colour and fluorescence emission spectrum. The detection limit was as low as 38 nM. Quenching mechanism was confirmed as photo-induced electron transfer (PET) by nuclear magnetic titration and DFT calculations. What's more, application in real water samples and solid phase paper tests illustrated the practical significance of detection of TNP in both vapor and solution.

Self-Assembly Hydrosoluble Coronenes: A Rich Source of Supramolecular Turn-On Fluorogenic Sensing Materials in Aqueous Media

Water-soluble coronenes, that form nanoparticles by self-association, work as new fluorescent materials by complexation with cucurbit[7]uril, as well as selective turn-on fluorogenic sensors for nitroaromatic explosives with remarkable selectivity, by using only water as solvent.

Dummy Molecularly Imprinted Polymers Using DNP as a Template Molecule for Explosive Sensing and Nitroaromatic Compound Discrimination

This work reports a rapid, simple and low-cost voltammetric sensor based on a dummy molecularly imprinted polymer (MIP) that uses 2,4-dinitrophenol (DNP) as a template for the quantification of 2,4,6-trinitrotoluene (TNT) and DNP, and the identification of related substances. Once the polymer was synthesised by thermal precipitation polymerisation, it was integrated onto a graphite epoxy composite (GEC) electrode via sol–gel immobilisation. Scanning electron microscopy (SEM) was performed in order to characterise the polymer and the sensor surface. Responses towards DNP and TNT were evaluated, displaying a linear response range of 1.5 to 8.0 µmol L−1 for DNP and 1.3 to 6.5 µmol L−1 for TNT; the estimated limits of detection were 0.59 µmol L−1 and 0.29 µmol L−1, for DNP and TNT, respectively. Chemometric tools, in particular principal component analysis (PCA), demonstrated the possibilities of the MIP-modified electrodes in nitroaromatic and potential interfering species discrimination with multiple potential applications in the environmental field.

Self-assembled porous nanoparticles based on silicone polymers with aggregation-induced emission for highly sensitive detection of nitroaromatics

Tetraphenylbenzene functionalized polysiloxane with AIE feature can self-assemble to unique porous structure and show high performance as fluorescent sensor.

Interpol review of detection and characterization of explosives and explosives residues 2016-2019

This review paper covers the forensic-relevant literature for the analysis and detection of explosives and explosives residues from 2016-2019 as a part of the 19th Interpol International Forensic Science Managers Symposium. The review papers are also available at the Interpol website at: https://www.interpol.int/Resources/Documents#Publications.

Fluorescent MoS2 QDs based on IFE for turn-off determination of FOX-7 in real water samples

A novel method for turn-off sensing 1,1-diamino-2,2-dinitroethylene (FOX-7) in aqueous medium was first proposed based on the inner filter effect (IFE) of FOX-7 on the fluorescence of molybdenum disulfide quantum dots (MoS₂ QDs). Water-soluble MoS₂ QDs as the fluorophore were prepared by the simple hydrothermal method. The morphology, structure, composition and optical properties of the prepared MoS₂ QDs were characterized by Transmission electron microscopy (TEM), Fourier transform infrared (FT-IR), X-ray photoelectron spectroscopy (XPS), UV-vis absorption and photoluminescence spectra. The results showed that the MoS₂ QDs had good water dispersibility and emitted strong photoluminescence with a particle size of 2 nm. Under the optimal experimental conditions, the fluorescence signal of MoS₂ QDs was quenched in the concentrations range of FOX-7 (0.5-100 μM) and the limit of detection (LOD) of the sensor was 0.19 μM. The method had been applied to analyze the real water samples with good selectivity and stability. Moreover, the quenching mechanism was studied systematically by the Fourier transform infrared (FT-IR), UV-vis absorption spectra, fluorescence lifetime, and Stern-Volmer equation, which had been proved to be static quenching. The fluorescence quenching mechanism is mainly IFE and electron transfer.

Sensing organic analytes by metal–organic frameworks: a new way of considering the topic

In this review, our goal is comparison of advantageous and disadvantageous of MOFs about signal-transduction in different instrumental methods for detection of different categories of organic analytes.

New perspective on the fluorescence and sensing mechanism of TNP chemosensor 2-(4,5-bis(4-chlorophenyl)-1H-imidazol-2-yl)-4-chlorolphenol

For TNP chemosensor 2-(4,5-Bis(4-Chlorophenyl)-1H-Imidazol-2-yl)-4-Chlorolphenol (HPICI), previous thought with no theoretical basis was that excited-state intramolecular proton transfer (ESIPT) process and the ground-state HPICI-TNP complex are mainly responsible for its fluorescence emission and the detection of TNP. However, this interpretation has been proved to be wrong by the present theoretical DFT/TDDFT explorations. Actually, the strong fluorescence of HPICI is mainly induced by the local excitation of the enol form HPICI(E) without ESIPT, and the fluorescence quenching by TNP is due to the photo-induced electron transfer (PET) process together with the cooperative effect of hydrogen-bonding interaction and π-π stacking interaction coexisting in the HPICI-TNP complex. The strengthened excited-state hydrogen bond promotes the PET process, thus facilitates the fluorescence quenching. This mechanism is proposed on the basis of the theoretical analyses on molecule geometry, binding energy, Gibbs free energy, electronic transitions, and frontier molecular orbitals (FMOs).

Rapid detection of TNP based on a commercial fluorescent probe

A simple, rapid and low cost sensing method for the fluorescent detection of TNP in 100% aqueous media was successfully developed based on a commercial probe. Under the non-covalent interactions between TNP with probe, a ratiometric output signal was achieved, which can be applied in real samples test.

Core-modified of fluoranthene with "propeller" structure for highly sensitive detection of nitroaromatic compounds

Two fluoranthene derivatives with "propeller" structure, named as 7,8,9,10-tetraphenylfluoranthene (TPFA) and 3-phenoxy-7,8,9,10-tetraphenyl fluoranthene (PO-TPFA), were designed and synthesized by introducing outer phenyl and phenoxy substituents to fluoranthene. Given the steric hindrance of this unique structure, both organic dyes exhibited similar fluorescence spectra and strong fluorescence emission from the solution to the film state. The introduction of a phenoxy group showed obvious influence to the molecular optical properties of fluoranthene. Density functional theory calculations were further conducted to verify this finding. Both dyes were used as fluorescent probes and exhibited and sensitive fluorescence response to nitroaromatic explosives and highly selectivity to picric acid. Furthermore, PO-TPFA exhibited better detection performance to nitroaromatic explosives than TPFA. This work can serve as a guide for molecular fluorescence design because these dyes possess excellent fluorescence in solution and film states and can be used for the sensitive fluorescence detection of nitroaromatic explosives.

Design of a Pyrene Scaffold Multifunctional Material: Real-Time Turn-On Chemosensor for Nitric Oxide, AIEE Behavior, and Detection of TNP Explosive

A dual-emission pyrene-based new fluorescent probe (N-(4-nitro-phenyl)-N'-pyren-1-ylmethyl-ene-ethane-1,2-diamine (PyDA-NP)) displays green fluorescence for nitric oxide (NO) sensing, whereas it exhibits blue emission in the aggregated state. The mechanism of nitric oxide (NO/NO+) sensing is based on N-nitrosation of aromatic secondary amine, which was not interfered by reactive oxygen species and reactive nitrogen species. The aggregation-induced enhancement of emission (AIEE) behaviors of the PyDA-NP could be attributed to the restriction of intramolecular rotation and vibration, resulting in rigidity enhancement of the molecules. The AIEE behavior of the probe was well established from fluorescence, dynamic light scattering, scanning electron microscopy, transmission electron microscopy, X-ray diffraction, optical fluorescence microscopy, and time-resolved photoluminescence studies. In a H2O/CH3CN binary mixture (8:2 v/v), the probe showed maximum aggregation with extensive (833-fold) increases in fluorescence intensity and high quantum yield (0.79). The aggregated state of the probe was further applied for the detection of nitroexplosives. It displayed efficient sensing of 2,4,6-trinitrophenol (TNP), corroborating mainly the charge-transfer process from pyrene to a highly electron-deficient TNP moiety. Furthermore, for the on-site practical application of the proposed analytical system, a contact-mode analysis was performed.

Two novel AIEE-active imidazole/ α-cyanostilbene derivatives: photophysical properties, reversible fluorescence switching, and detection of explosives

Novel imidazole derivatives containing the α-cyanostilbene unit can act as reversible acid/base stimulated fluorescence switches in the solid state, as chemosensors for explosives detection in aqueous systems, and as test strip detectors.

Synthesis of tetraphenylethylene-based conjugated microporous polymers for detection of nitroaromatic explosive compounds

Conjugated microporous polymers (CMPs) containing tetraphenylethylene (TPE) were synthesized via the Suzuki coupling polymerization.

Strong Blue Emissive Supramolecular Self-Assembly System Based on Naphthalimide Derivatives and Its Ability of Detection and Removal of 2,4,6-Trinitrophenol

Two simple and novel gelators (G-P with pyridine and G-B with benzene) with different C-4 substitution groups on naphthalimide derivatives have been designed and characterized. Two gelators could form organogels in some solvents or mixed solvents. The self-assembly processes of G-P in a mixed solvent of acetonitrile/H₂O (1/1, v/v) and G-B in acetonitrile were studied by means of electron microscopy and spectroscopy. The organogel of G-P in the mixed solvent of acetonitrile/H₂O (1/1, v/v) formed an intertwined fiber network, and its emission spectrum had an obvious blue shift compared with that of solution. By contrast, the organogel of G-B in acetonitrile formed a straight fiber, and its emission had an obvious red shift compared with that of solution. G-P and G-B were employed in detecting nitroaromatic compounds because of their electron-rich property. G-P is more sensitive and selective toward 2,4,6-trinitrophenol (TNP) compared with G-B. The sensing mechanisms were investigated by ¹H NMR spectroscopic experiments and theoretical calculations. From these experimental results, it is proposed that electron transfer occurs from the electron-rich G-P molecule to the electron-deficient TNP because of the possibility of complex formation between G-P and TNP. The G-P molecule could detect TNP in water, organic solvent media, as well as using test strips. It is worth mentioning that the organogel G-P can not only detect TNP but also remove TNP from the solution into the organogel system.