Detection Of TNT Research Articles

Detection of TNT based on conjugated polymer encapsulated in mesoporous silica nanoparticles through FRET

Amine-functionalized mesoporous silica nanoparticles containing poly(p-phenylenevinylene) provide a facile strategy to detect TNT through fluorescence resonance energy transfer (FRET). The observed linear fluorescence intensity change allows the quantitative detection of TNT with the detection limit of 6 × 10(-7) M.

Highly efficient SERS substrate for direct detection of explosive TNT using popcorn-shaped gold nanoparticle-functionalized SWCNT hybrid

This paper reports for the first time the development of a large-scale SERS substrate from a popcorn-shaped gold nanoparticle-functionalized single walled carbon nanotubes hybrid thin film for the selective and highly sensitive detection of explosive TNT material at a 100 femtomolar (fM) level.

TNT Vapor Detection Based on a Lab-on-a-Fiber: Achieving a Millimeter-Scale Sensing Element on Fiber

In this paper, we discuss in detail the lab-on-a-flber (LOF) concept that we proposed earlier (Ma et ah, Proc. 4th Eur. Workshop Opt. Fiber Sens., 2010, vol. 7653, PP. 76531E-76531E-4), and present a specific example of this platform intended for trace vapor TNT detection. We show how we arrive at the current LOF design by examining the performance, technical difficulties, and complexities of various possible architectures. In the design solution adopted in our example, the sensing section occupies a space measuring only 1.6 × 1.6 × 0.8 mm, but contains several optical and chemical components/functions including a transmission/reflection mirror and TNT sensory film coated on a segment of the side wall of the fiber core. The fiber itself thus serves as the film substrate and when coated with the film becomes an evanescent-wave form fluorescent emission power collector. Its tiny dimensions notwithstanding, the LOF performs several simultaneous functions, including power density tuning and stray excitation light blocking. In addition, this LOF platform features ease of system construction and polymer film application. We demonstrate its fast response to TNT vapor, in the form of a 29% signal drop after 10 s of exposure.

Fluorescent conjugated polycarbazoles for explosives detection: Side chain effects on TNT sensor sensitivity

Considering electronic and structural interactions between fluorescent polymers and TNT, we have designed and synthesized two carbazole-based polymers (P1 and P2), possessing 2-ethylhexyl and 4-[tris-(4-octyloxyphenyl)methyl]phenyl as side chains, respectively. The distinct side chains cause dramatic differences in the polymer sensing behavior. It is demonstrated that large and more rigid side chains could reduce the interactions between polymer chains in the solid state, while supporting the diffusion of explosives through more accessible space, thereby contributing to the sensitivity. Furthermore, we have proved that bulky side chains obviously did not influence the conformation of the backbone, which is necessary for the conjugated polymers to act as fluorescent sensing material. The results suggest that P2 is a promising material for TNT detection with pronounced sensitivity, in addition they provide a new design-thought for TNT sensing materials.

Enhanced electrocatalytic activity of nitrogen-doped graphene for the reduction of nitro explosives

Nitrogen-doped graphene (NG) shows enhanced electrocatalytic activity toward the reduction of nitroaromatic compounds with a decreased overpotential (ca. 20mV) compared with thermally reduced graphene (TR-G) and thus a NG-based sensing platform for sensitively electrochemical detection of TNT with a lower detection limit has been constructed. This prominent electrocatalytic activity of NG could be ascribed to the pyridine-like nitrogen atoms existing at the edge plane of graphene sheets.

A colorimetric sensor based on anodized aluminum oxide (AAO) substrate for the detection of nitroaromatics

Simple and low cost colorimetric sensors for explosives detection were explored and developed. Anodized aluminum oxide (AAO) with large surface area through its porous structure and light background color was utilized as the substrate for colorimetric sensors. Fabricated thin AAO films with thickness less than ∼500 nm allowed us to observe interference colors which were used as the background color for colorimetric detection. AAO thin films with various thickness and pore-to-pore distance were prepared through anodizing aluminum foils at different voltages and times in dilute sulfuric acid. Various interference colors were observed on these samples due to their difference in structures. Accordingly, suitable anodization conditions that produce AAO samples with desired light background colors for optical applications were obtained. Thin film interference model was applied to analyze the UV–vis reflectance spectra and to estimate the thickness of the AAO membranes. We found that the thickness of produced AAO films increased linearly with anodization time in sulfuric acid. In addition, the growth rate was higher for AAO anodized using higher voltages. The thin film interference formulism was further validated with a well established layer by layer deposition technique. Coating poly(styrene sulfonate) sodium salt (PSS) and poly(allylamine hydrochloride) (PAH) layer by layer on AAO thin film consistently shifted its surface color toward red due to the increase in thickness. The red shift of UV–vis reflectance was correlated quantitatively to the number of layers been assembled. This sensitive red shift due to molecular attachment (increase in thickness) on AAO substrate was applied toward nitroaromatics detection. Aminopropyltrimethoxysilane (APTS) which can be attached onto AAO nanowells covalently through silanization and attract TNT molecules was coated and applied for TNT detection. UV–vis spectra of AAO with APTS shifted to the longer wavelength side due to TNT attachment. This red shift implied AAO thickness increased and positive detection of TNT molecules. It was also observed that both APTS and polyethyleneimine (PEI) were electron rich polymers which formed Meisenheimer complexes with TNT in solution and changed its color abruptly. This strong color change due to chemical reaction was applied as another approach for direct TNT detection. Commercial AAO films with long pores (60 μm) and white background color were coated with APTS or PEI and then exposed to TNT in solution. These membranes turned to pink rapidly and eventually became visibly orange after a few hours with a strong absorption around 500 nm that was consistent with the formation of Meisenheimer complexes. The visible color change can be observed by unaided eyes and is suitable for nitroaromatics detection at higher concentration while interference color red shift in AAO thin film is designed for nitroaromatics detection at monolayer (nm) level.

Optical bandgaps and fluorescence resonance energy transfer studies of a series of poly(phenyleneethynylene) derivatives

In this paper, research work focuses on the synthesis of a series of PPE-based polymers with commonly used conjugated units, including thiophene, benzo[c][1,2,5]thiadiazole (BT), benzo[c][1,2,5]selenadiazole (BSe), etc. The optical bandgaps of these polymers were tuned in the range of 2.10–2.76 eV. The order of bandgap-lowering ability of these units in PPE-derivatives is: M-3 > M-6 > M-5 > M-4 > M-9 ⩾ M-7, M-8 > M-2. Their FRET applications in polymer solar cell and TNT detection were studied respectively, and the results indicated that all these PPE-derivatives were good candidate materials for polymer solar cells or detecting TNT in solution. Furthermore, if electron-acceptor units had structures similar to the diphenylquinoxaline in the PPE-derivatives chain, the polymers would give a better fluorescence quenching in response to TNT compound. Polymers PPE-7 and PPE-8 were chosen as representative samples to investigate their photo-oxidative stability compared with that of PPVs or PTs. The results demonstrated that both polymers PPE-7 and PPE-8 were more photo-oxidatively stable than MEH-PPV or P3HT.

Selective Detection of TNT and Picric Acid by Conjugated Polymer Film Sensors with Donor–Acceptor Architecture

Selective Detection of TNT and Picric Acid by Conjugated Polymer Film Sensors with Donor–Acceptor Architecture

Two-dimensional molecular imprinting approach for the electrochemical detection of trinitrotoluene

In this work, we demonstrated a sensitive and selective electrochemical sensing protocol for the detection of TNT prepared from alkanethiols self-assembled on AuNPs modified glassy carbon (GC) electrode with preadsorbed templates of TNT. It demonstrated that the 2D molecular imprinting monolayers (MIMs) can provide a better site accessibility and lower mass-transfer resistance, while the AuNPs can enhance electrode conductivity, facilitate the electron transfer and increase the amount of TNT-imprinted sites. The prepared sensor showed not only high selectivity toward TNT in comparison to other similar nitroaromatic compounds (NACs), but also a wide linear range over TNT concentration from 4.0 × 10 −8 to 3.2 × 10 −6 M with a detection limit of 1.3 × 10 −8 M (S/N = 3). Moreover, the imprinted sensor has been applied to the determination of TNT in spiked environmental water samples and shows promise for fast and sensitive measurement of trace levels of TNT in real samples.

Electrochemical detection of TNT with in-line pre-concentration using imprinted diethylbenzene-bridged periodic mesoporous organosilicas

We examined the adsorption and release of TNT using diethylbenzene-bridged (DEB) periodic mesoporous organosilica sorbents under varying conditions. The sorbents were applied for in-line target pre-concentration in conjunction with an electrochemical flow cell containing a glassy carbon electrode. Square wave voltammetry was employed for TNT detection. TNT sample volumes between 2 and 480 mL at concentrations ranging from 0.5 to 500 ppb were passed through the DEB sorbents (imprinted or not imprinted for TNT) at pH 6 (sodium acetate) or at pH 7.4 (PBS). Release of target was accomplished using solvent mixtures of methanol/water with sodium acetate as electrolyte or acetonitrile/water with PBS components as electrolyte. Under these conditions, the TNT was released in <200 μL of the solvent mixture, and pre-concentration factors of >3000 can be achieved when using large volumes of trace TNT samples. When sample volumes of 2 mL were utilized, the sensing system gave a linear response between 20 and 500 ppb with an estimated limit of detection of 13 ppb. When pre-concentrating 480 mL of sample in either buffered solution or seawater, detection of 0.5 ppb TNT was achieved with a signal to noise ratio of 20.

Amplifying fluorescence sensing based on inverse opal photonic crystal toward trace TNT detection

A fluorescence-amplifying method based on photonic crystal (PC) has been demonstrated for trace TNT detection. The fluorescence enhancement for TNT detection on the optimized PC can be up to 60.6-fold in comparison to that of the control sample, which combines the slow photon effect of PC and large surface areas of the inverse opal structure. Furthermore, the quenching efficiency of the PC-based sensor achieves 80% after exposure to TNT vapor for 300 s. The results suggest that the fluorescence-amplifying method based on PC has enormous potential for the development of highly efficient fluorescence sensors toward detection of trace TNT or other explosives.

Plasmonic resonance energy transfer-based nanospectroscopy for sensitive and selective detection of 2,4,6-trinitrotoluene (TNT)

Here we report sensitive and selective detection of TNT based on plasmonic resonance energy transfer from a gold nanoplasmonic probe to conjugated target TNT molecules, leading to quenching on the Rayleigh scattering spectrum of the probe.

Detection of TNT explosives with a new fluorescent conjugated polycarbazole polymer

A novel fluorescent poly(2,7-carbazole) with a 4-[tris-(4-octyloxyphenyl)methyl]phenyl side chain is used to detect the explosive compounds TNT and DNT. It shows high recycled fluorescence quenching sensitivity, which is due to its strong electron donating ability and weaker interaction between the polymer chains caused by the bulky side chain.

Syntheses and characterization of amplified fluorescence poly(aryleneethynylene)s based on 3,4-propylenedioxythiophenes and their application in TNT sensing

A series of electron rich dialkylated 3,4-propylenedioxythiophenes (ProDOT) based poly(aryleneethynylene), PAE, were synthesized and characterized in order to increase the absorption and emission maxima as compared to the their wholly phenylene based counterparts. As planned, these new polymers showed absorption maximum in the range of 397–432 nm with emission wavelength in the range of 511–559 nm which is significantly red shifted compared to the phenylene based PAE. Though, the absorption and emission maxima in this new series of PAEs was significantly red shifted, the quantum yields were found to be much lower as compared to the wholly phenylene based PAEs. The quantum yields were improved by the incorporation of bulky pentiptycene moiety which also resulted in fluorescence in solid state thin films. Furthermore, incorporation of pentiptycene units results in the binding of small aromatic compounds such as TNT resulting in the detection of TNT in thin films by fluorescence quenching. It was interesting to note that these pentiptycene based polymers on incorporation of ProDOTs exhibited lower quantum yields when compared with corresponding wholly phenylene based counterparts. This was attributed to the heavy atom effect due to the presence of sulphur in ProDOT. A series of copolymers were synthesized incorporating various amounts of ProDOT in order to explore if it is possible to increase quantum yield while retaining ProDOT in the final copolymer. However, results indicated that the incorporation of even small amount of ProDOT results in significant lowering of the quantum yields. All these polymers were characterized using NMR, FTIR, GPC, UV–Vis and fluorescence spectroscopy.

Ultrasensitive SERS Detection of TNT by Imprinting Molecular Recognition Using a New Type of Stable Substrate

We report herein a method for the ultra-trace detection of TNT on p-aminothiophenol-functionalized silver nanoparticles coated on silver molybdate nanowires based on surface-enhanced Raman scattering (SERS). The method relies on π-donor-acceptor interactions between the π-acceptor TNT and the π-donor p,p'-dimercaptoazobenzene (DMAB), with the latter serving to cross-link the silver nanoparticles deposited on the silver molybdate nanowires. This system presents optimal imprint molecule contours, with the DMAB forming imprint molecule sites that constitute SERS "hot spots". Anchoring of the TNT analyte at these sites leads to a pronounced intensification of its Raman emission. We demonstrate that TNT concentrations as low as 10(-12) M can be accurately detected using the described SERS assay. Most impressively, acting as a new type of SERS substrate, the silver/silver molybdate nanowires complex can yield new silver nanoparticles during the detection process, which makes the Raman signals very stable. A detailed mechanism for the observed SERS intensity change is discussed. Our experiments show that TNT can be detected quickly and accurately with ultra-high sensitivity, selectivity, reusability, and stability. The results reported herein may not only lead to many applications in SERS techniques, but might also form the basis of a new concept for a molecular imprinting strategy.

Dipyrenylcalix[4]arene—A Fluorescence‐Based Chemosensor for Trinitroaromatic Explosives

A new chemosensor-based approach to the detection of nitroaromatics is described. It involves the analyte-induced quenching of excimer emission of a dipyrenyl calix[4]arene (L). The chemical and photophysical properties of the complexes formed between L and mono-, di-, and trinitrobenzene, and di- and trinitrotoluene were studied in acetonitrile and chloroform by using (1)H NMR, UV/Vis, and fluorescence spectroscopy. Fluorescence spectroscopy revealed that the trinitroaromatics engendered the largest response among the various substrates tested, with the sensitivity for these analytes being correspondingly high. Quantitative analysis of the fluorescence titration profile generated from the titration of L with TNT provided evidence that this particular functionalized calix[4]arene receptor allows for the detection of TNT down to the low ppb level in CH(3)CN. A single-crystal X-ray diffraction analysis revealed that in the solid state the complex L.TNT consists of a supramolecular crystalline polymeric structure, the formation of which appears to be driven by intermolecular pi-pi interactions between two pyrene units and a TNT molecule held at a distance of 3.2-3.6 A, as well as by intra- and intermolecular hydrogen-bonds among the amide linkages. Nevertheless, the changes in the (1)H NMR, UV/Vis, and fluorescence spectrum, including sharp color changes, are ascribed to a charge-transfer interaction arising from complementary pi-pi overlap between the pyrene subunits and the bound trinitroaromatic substrates. A number of ab initio calculations were also carried out and, considered in concert, they provide further support for the proposed charge-transfer interactions, particularly in the case of L.TNT.

L-cysteine-capped CdTe QD-based sensor for simple and selective detection oftrinitrotoluene

Trinitrotoluene, usually known as TNT, is a kind of chemical explosive with hazardous andtoxic effects on the environment and human health. National and societal security concernshave dictated an increasing need for the analytical detection of TNT with rapidity, highsensitivity and low cost. This work demonstrates a novel method using L-cysteine-cappedCdTe quantum dots (QDs) to assay TNT, based on the formation of a Meisenheimercomplex between TNT and cysteine. The fluorescence (FL) of quantum dots quenchbecause electrons of the QDs transfer to the TNT molecules via the formation of aMeisenheimer complex. TNT can be detected with a low detection limit of 1.1 nM.Studies on the selectivity of this method show that only TNT can generate anintense signal response. The synthesized QDs are excellent nanomaterials for TNTdetection. In addition, TNT in soil samples is also analyzed by the proposed method.

Detection and identification of TNT, 2,4-DNT and 2,6-DNT by near-infrared cavity ringdown spectroscopy

A dedicated instrument based on cw cavity ringdown (CRD) spectroscopy has been used to study the feasibility of solid explosive detection in the near infrared. A flash heater was used to evaporate solid samples in a CRD absorption cell. The vapor phase spectra of TNT, 2,4-DNT and 2,6-DNT have been recorded for the first time in the spectral range between 1560 and 1680 nm. Although the three explosives are chemically very similar the recorded spectra are distinct and permit an unambiguous identification of the three pure substances. The fast sample preparation and short detection times render the technique useful for trace detection of solid particles. The detection sensitivity is estimated in the 10–100 ng range and is adequate for trace detection and identification of solid explosives.

Hollow silica nanospheres containing a silafluorene–fluorene conjugated polymer for aqueous TNT and RDX detection

Attachment of a copolymer of silafluorene and fluorene to 100 nm hollow silica nanoparticles provides a new method to detect aqueous TNT and RDX with a low detection limit using the suspended fluorescent nanoshells.

A Hybrid Nanosensor for TNT Vapor Detection

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