The Detection Of 2,4,6-trinitrotoluene Research Articles

Selective aptasensor for trinitrotoluene detection: Comparison of the detecting performances from liquid and vapor phases

In general, chromatographic and sensor analyses have been utilized for explosive detection. The main interest on those systems is to develop a method to selectively detect explosives at a single step as well as from vapor phase if possible. Moreover, on-site and real-time detection with portable systems is another challenge for the researchers. On the other hand, the detection of 2,4,6-trinitrotoluene (TNT) vapor at the crime scene, preferably before the explosion is highly demanded in order to prevent the negative effects of terrorism and to ensure the safety of the civilian population. In this study, initially, Quartz Crystal Microbalance (QCM) sensor was prepared for real-time monitoring of TNT in aqueous solution, through the attachment of TNT peptide aptamer on the gold surface of QCM sensor. Secondly, after providing optimum conditions, TNT detection was investigated even from vapor phase through the QCM aptasensor. According to results, the selectivity coefficient of QCM-based aptasensor was calculated as 6.78 for TNT in respect to DNT whereas that was calculated as 9.02 for TNT in respect to TNB. In addition, the evaluation of the reusability and storage stability emphasized that the sensor could be used repeatedly without significant reduction in dissipation (∆D) values. The linearity coefficient (R2) was found to be 0.9965. The limit of detection (LOD) and the limit of quantitation (LOQ) were determined as 0.0238 and 0.0739 nM, respectively. The studies demonstrated that the portable QCM sensor decorated with the aptamer selective for TNT molecules could be classified as a promising alternative, selective, cost-friendly, easy-to-prepare, ready-to-use, and applicable for on-site and real-time explosive measurements (even from vapor phase).

Enhancing DNT Detection by a Bacterial Bioreporter: Directed Evolution of the Transcriptional Activator YhaJ.

Detection of buried landmines is a dangerous and complicated task that consumes large financial resources and poses significant risks to the personnel involved. A potential alternative to conventional detection methodologies is the use of microbial bioreporters, capable of emitting an optical signal upon exposure to explosives, thus revealing to a remote detector the location of buried explosive devices. We have previously reported the design, construction, and optimization of an Escherichia coli-based bioreporter for the detection of 2,4,6-trinitrotoluene (TNT) and its accompanying impurity 2,4-dinitrotoluene (DNT). Here we describe the further enhancement of this bioreporter by the directed evolution of YhaJ, the transcriptional activator of the yqjF gene promoter, the sensing element of the bioreporter’s molecular circuit. This process resulted in a 37-fold reduction of the detection threshold, as well as significant enhancements to signal intensity and response time, rendering this sensor strain more suitable for detecting the minute concentrations of DNT in the soil above buried landmines. The capability of this enhanced bioreporter to detect DNT buried in sand is demonstrated.

3D-printing pen versus desktop 3D-printers: Fabrication of carbon black/polylactic acid electrodes for single-drop detection of 2,4,6-trinitrotoluene

The fabrication of carbon black/polylactic acid (PLA) electrodes using a 3D printing pen is presented and compared with electrodes obtained by a desktop fused deposition modelling (FDM) 3D printer. The 3D pen was used for the fast production of electrodes in two designs using customized 3D printed parts to act as template and guide the reproducible application of the 3D pen: (i) a single working electrode at the bottom of a 3D-printed cylindrical body and (ii) a three-electrode system on a 3D-printed planar substrate. Both devices were electrochemically characterized using the redox probe [Fe(CN)6]3−/4- via cyclic voltammetry, which presented similar performance to an FDM 3D-printed electrode or a commercial screen-printed carbon electrode (SPE) regarding peak-to-peak separation (ΔEp) and current density. The surface treatment of the carbon black/PLA electrodes fabricated by both 3D pen and FDM 3D-printing procedures provided substantial improvement of the electrochemical activity by removing excess of PLA, which was confirmed by scanning electron microscopic images for electrodes fabricated by both procedures. Structural defects were not inserted after the electrochemical treatment as shown by Raman spectra (iD/iG), which indicates that the use of 3D pen can replace desktop 3D printers for electrode fabrication. Inter-electrode precision for the best device fabricated using the 3D pen (three-electrode system) was 4% (n = 5) considering current density and anodic peak potential for the redox probe. This device was applied for the detection of 2,4,6-trinitrotoluene (TNT) via square-wave voltammetry of a single-drop of 100 μL placed upon the thee-electrode system, resulting in three reduction peaks commonly verified for TNT on carbon electrodes. Limit of detection of 1.5 μmol L−1, linear range from 5 to 500 μmol L−1 and RSD lower than 4% for 10 repetitive measurements of 100 μmol L−1 TNT were obtained. The proposed devices can be reused after polishing on sandpaper generating new electrode surfaces, which is an extra advantage over chemically-modified electrochemical sensors applied for TNT detection.

A bioinspired peptide matrix for the detection of 2,4,6-trinitrotoluene (TNT)

A novel peptide-based three-dimensional probe called “peptide matrix,” inspired by the antibody paratope region, was fabricated on a surface plasmon resonance (SPR) sensor chip to enhance the sensitivity of detecting the explosive 2,4,6-trinitrotoluene (TNT). Although peptide aptamer is an attractive candidate for a molecular recognition probe because of its ease of synthesis and chemical stability, it still has difficulty in applying to highly sensitive (i.e. parts-per-billion (ppb) or sub-ppb level) detections. Thus, we developed the concept of peptide matrix structure, which is constructed by consecutive disulfide bond formation between a large number of peptide fragments. This robust three-dimensional structure displays multiple binding sites which can efficiently associate with each TNT molecule. The peptide matrix lowered the dissociation constant (KD) by two orders of magnitude compared to the linear peptide aptamer, estimating KD as 10.1 nM, which is the lowest concentration reported by using peptide-based TNT probe. Furthermore, the concentration limit of detection of peptide matrix modified SPR sensor was 0.62 ppb, and hence comparable to single-chain variable fragment (scFv)-based TNT sensors. To our knowledge, this is the first report demonstrating peptide matrix fabrication and its application for small explosive molecule detection. This peptide matrix-based approach, which has the advantage of simple synthesis and high sensitivity, will be applicable to many other small-molecule label-free detections.

Efficient Sensing of Trinitrotoluene Using a Photoluminescent Benzo[a]fluorenone Derivative

AbstractHerein, we have presented a simple organic compound, benzo[a]fluorenone, as a highly fluorescent chemosensor for the detection of 2,4,6‐trinitrotoluene (TNT) in solution phase with a limit of detection (LOD) down to 4 nM. This probe is more sensitive towards TNT than 2,4‐dinitrotoluene (DNT) and picric acid (PA). The photophysical studies revealed that it is static quenching through a ground state interaction between TNT and the title compound.

Smart Sensor Using Cellulose-Based Material for TNT Detection

A smart sensor with cellulose-based material was developed for the detection of 2,4,6-trinitrotoluene (TNT), using potassium hydroxide/ethanol reagent adsorbed onto a cellulose cotton swab. A red color was observed immediately after exposure to TNT. The sensor allowed rapid qualitative and semi-quantitative analysis of TNT by naked-eye, observation at TNT amounts > 2 μg. To improve precision and accuracy, a smartphone was used to capture digital images of the color. A calibration curve was constructed between log TNT (μg) vs. color intensity, and was linear in the range 1-30 μg-TNT with R2= 0.9975. The limit of detection (3.3σ/slope) was 0.11 μg-TNT and percentage relative standard deviation (%RSD, n=10) was 2.30. The sensor was used to detect the TNT samples of soil and from non-porous and porous surfaces.

Downconversion Luminescence-Based Nanosensor for Label-Free Detection of Explosives.

We report a selective and sensitive nanosensor probe based on polyethylenimine (PEI)-capped downconverting nanophosphors β-NaYF4:Gd3+,Tb3+@PEI for the detection of 2,4,6-trinitrotoluene (TNT), both in water and buffer media. These downconverting phosphors were synthesized via a hydrothermal route and are known to show excellent chemical, thermal, and photostability. They emit sharp emission peaks centered at ∼488, 544, 584, and 619 nm, among which the peak at ∼544 nm was remarkably quenched (∼90%) by the addition of TNT without giving any new emission peak. The sensing mechanism is based on the formation of a Meisenheimer complex between the electron-rich amine-functionalized β-NaYF4:Gd3+,Tb3+ nanophosphors and electron-deficient TNT molecule, which was prominently visualized by the change in the color of the solution from whitish to brownish yellow, enabling visual detection, followed by luminescence resonance energy transfer between the nanophosphors and the complex. A linear range for TNT detection was obtained from 0.1 to 300 μM with a limit of detection as low as 119.9 nM. This method displayed excellent selectivity toward TNT over other nitroaromatic compounds, which had no influence on the detection. Moreover, various other classes of analytes, viz., amino acids, pesticides, and sugars, did not quench the luminescence intensity of the nanophosphors. This developed nanosensor probe possesses high, stable fluorescence brightness and capability for the selective and sensitive on-site recognition of TNT molecules in aqueous media, avoiding complicated strategies and instruments. Thus, this work promises to pave ways to many applications in the detection of ultratrace analytes.

SPR Enhanced molecular imprinted sol–gel film: A promising tool for gas-phase TNT detection

An innovative surface plasmon resonance (SPR) approach for the detection of 2,4,6-trinitrotoluene (TNT) gas traces, obtained using an engineered molecular imprinted sol–gel film as recognition layer onto a plasmonic gold grating, is here proposed. The SPR substrate combined with the sol–gel matrix is able to trap gas phase TNT molecules from a TNT-saturated environment (4.9ppb). Taking advantage of the azimuthally-controlled grating-coupled SPR, this sensing platform demonstrates the potentiality to detect TNT traces <1ppb with a sensitivity of 0.47°/ppb.

Rapid and Specific Aqueous-Phase Detection of Nitroaromatic Explosives with Inherent Porphyrin Recognition Sites in Metal-Organic Frameworks.

Development of a rapid and effective method for the detection of 2,4,6-trinitrotoluene (TNT) in aqueous phase has attracted great attention. In this work, the fluorescent porphyrin-based metal-organic frameworks (MOFs) of PCN-224 were successfully exploited as a fluorescent probe for the rapid and selective TNT detection in water media. This strategy combined the advantages of fluorescent porphyrin molecules and porous MOFs, which not only overcame the aggregation of hydrophobic tetrakis(4-carboxyphenyl)porphyrin (TCPP) recognition sites but also promoted TNT to interact with recognition sites in virtue of the high surface and intrinsic open structure of MOFs. As a result, a rapid response time of as short as 30 s was obtained for the elaborated fluorescent probe. Meanwhile, the bright red emission of porphyrin units in PCN-224 could be proportionally quenched in correlation with the applied TNT level through the formation of TNT-TCPP complex in the ground state. The specificity of the employed sensory platform for TNT recognition was scarcely affected by other possible coexistent interfering species. Furthermore, this fluorescent PCN-224 probe presented a much higher quenching efficiency for TNT than other structurally similar nitroaromatic compounds and was successfully applied for the quantitative detection of TNT in the mixed nitroaromatic explosive samples. This prefigured their great potentials of practical TNT detection in water media for public safety and security.

Improvement of Explosive Detection with a Fluorescent Sensor Using a Heating Device

There is a strong demand for a fast and reliable detection of explosives because of their use in most terrorist attacks. Chemical sensors, especially fluorescent ones, seem to fill the need in terms of reliability, cost and handling ability. In this paper, the detection of 2,4,6-trinitrotoluene (TNT) and 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX or hexogen) using a heating device of the particles was studied. Two fluorescent sensitive materials were compared: diimine [1] and polycarbosilane functionalised with pyrene moieties at 50% (PCS-Py-50%) [2]. Both materials were shown to be sensitive to TNT and RDX vapours. The PCS-Py-50% material was the most promising for the detection of RDX because of a higher kinetics of interaction.

Upconversion luminescence nanosensor for TNT selective and label-free quantification in the mixture of nitroaromatic explosives

This paper reports a rapid, sensitive, and selective nanosensor for the detection of 2,4,6-trinitrotoluene (TNT) in the mixture aqueous solution of nitroaromatics independent of immunoassay or molecularly imprinted technology and complicated instruments. Despite many strategies including immunoassay and molecularly imprinted technologies been successfully developed for the detection of TNT, it is not easy to differentiate TNT from 2,4,6-trinitrophenol (TNP) due to their very similar chemical structures and properties. In this work, the amine functionalized NaYF4:Yb(3+)/Er(3+) upconversion luminescence nanoparticles (UCNPs) whose excitation (980 nm) and emission (543 nm) wavelength were far from the absorbance bands of other usual interference nitroaromatics including 2,4-dinitrotoluene (DNT), nitrobenzene (NB), and especially TNP, were utilized as the luminescent nanosensors for TNT luminescence detection. To make these UCNPs highly water stable and render the charge transfer from UCNPs to TNT easier, amino groups were introduced onto the surface of the UCNPs by coating a polymer layer of ethylene glycol dimethacrylate (EGDMA) hybridized with 3-aminopropyltriethoxysilane (APTS). After binding with TNT through amino groups on the UCNPs, the naked eye visible green upconversion luminescence of the UCNPs was dramatically quenched and thus a sensitive UC luminescence nanosensor was developed for TNT detection. However, other nitroaromatics including TNP, DNT, and NB have no influence on the green UC luminescence and thus no influence on the TNT detection. The luminescence intensity is negatively proportional to the concentration of TNT in the range of 0.01-9.0 µg/mL with the 3σ limit of detection (LOD) of 9.7 ng/mL. The present studies provide a novel and facile strategy to fabricate the upconversion luminescence sensors with highly selective recognition ability in aqueous media and are desirable for label free analysis of TNT in mixed solution independent of immunoassay and molecularly imprinted technology and complicated instruments.

An ultra-sensitive piezoresistive polymer nano-composite microcantilever sensor electronic nose platform for explosive vapor detection

In the present paper, we demonstrate a compact, nonoptical, and inexpensive polymer nano-composite microcantilever sensor platform for the detection of 2,4,6-trinitrotoluene (TNT), hexahydro-1,3,5-triazine (RDX) and pentaerythritol tetranitrate (PETN) vapors at room temperature. In order to achieve sufficient selectivity, the piezoresistive polymer nano-composite microcantilevers coated with gold surfaces are modified with self-assembled monolayers (SAM) of 4-mercaptobenzoic acid (4-MBA), 6-mercaptonicotonic acid (6-MNA) and 2-mercaptonicotonic acid (2-MNA). The SAMs formation is confirmed by FTIR and contact angle measurements. The ultrahigh sensitive piezoresistive polymer nano-composite microcantilever provides detection sensitivities in the below parts-per-trillion level within few seconds of exposure under ambient conditions. Maximum bending of the microcantilever is achieved within 20s with response and recovery time of ∼3s and 4s, respectively. The cross selectivity of 4-MBA and 6-MNA coated microcantilevers is confirmed by investigating exposure to different organic compounds. We also demonstrate that the polymer nano-composite microcantilever is ideally suited for “electronic nose” applications. Further, the ultra-high sensitivity and low cost of polymer nano-composite microcantilever can lead to the development of a rugged portable, handheld device for rapid and sensitive detection of explosive vapors.

Graphenes prepared from multi-walled carbon nanotubes and stacked graphene nanofibers for detection of 2,4,6-trinitrotoluene (TNT) in seawater

The study on explosive materials is paramount due to the potential hazards to national security and health. When disposed of, explosives can cause seawater pollution. The detection of 2,4,6-trinitrotoluene (TNT) in seawater has been examined on two different forms of graphene, mainly graphene prepared from the unzipping of multi-walled carbon nanotubes (MWCNTs) and from the exfoliation of stacked graphene nanofibers (SGNFs). Graphene sheets prepared from MWCNTs exhibited sheet dimensions of 5000 × 300 nm, while graphene prepared from SGNFs exhibited sheet dimensions of 50 × 50 nm. Graphene prepared from MWCNTs was found to exhibit a higher order of sensitivity than the one prepared from nanofibers in both borate buffer solution and seawater. We demonstrate that it is of high importance to study different sources and methods of preparation of graphenes for analytical chemistry applications.

Make it different: The plasma treated multi-walled carbon nanotubes improve electrochemical performances toward nitroaromatic compounds

On the basis of plasma treatment method, O2-plasma-treated multi-walled carbon nanotubes (po-MWCNTs) and NH3-plasma-treated multi-walled carbon nanotubes (pn-MWCNTs) were used for electrochemical detection of nitroaromatic compounds (NACs) and showed enhanced sensitivity compared with raw MWCNTs. The difference of electrochemical response toward NACs between po-MWCNTs and pn-MWCNTs was observed and systematically compared in this work for the first time. Square wave adsorptive stripping voltammetry has been used for the detection of 2,4,6-trinitrotoluene (TNT), 2,4-dinitrotoluene (2,4-DNT) and 4-nitrotoluene (4-NT). By comparing the electrochemical performance toward the three different NACs, it was found that the different number of nitro groups on aromatic ring can cause different sensitivity at the po-MWCNTs and pn-MWCNTs electrodes. The detection limit (3σ method) of both the po-MWCNTs and the pn-MWCNTs electrodes was below nM level. The chemical and electrochemical parameters that exert influence on oxidation–reduction reaction of NACs, such as supporting electrolytes, pH value, and deposition time, were carefully studied. The difference between po-MWCNTs and pn-MWCNTs electrodes indicated that different functional groups on MWCNTs surface may result in the different electrochemical responses toward NACs, which enlighten the area of functionalizing the MWCNTs for detecting NACs. In addition, the possible mechanisms based on adsorption have been proposed. The electrochemical behavior and adsorption ability are closely bound up.

Development of a chemiluminescence-based quantitative lateral flow immunoassay for on-field detection of 2,4,6-trinitrotoluene

Simple, rapid and highly sensitive assays, possibly allowing on-site analysis, are required in the security and forensic fields or to obtain early signs of environmental pollution. Several bioanalytical methods and biosensors based on portable devices have been developed for this purpose. Among them, Lateral Flow ImmunoAssays (LFIAs) offer the advantages of rapidity and ease of use and, thanks to the high specificity of antigen–antibody binding, allow greatly simplifying and reducing sample pre-analytical treatments. However, LFIAs usually employ colloidal gold or latex beads as labels and they rely on the formation of colored bands visible by the naked eye. With this assay format, only qualitative or semi-quantitative information can be obtained and low sensitivity is achieved. Recently, the use of enzyme-catalyzed chemiluminescence detection in LFIA has been proposed to overcome these problems. In this work, we describe the development of a quantitative CL-LFIA assay for the detection of 2,4,6-trinitrotoluene (TNT) in real samples. Thanks to the use of a portable imaging device for CL signal measurement based on a thermoelectrically cooled CCD camera, the analysis could be performed directly on-field. A limit of detection of 0.2μgmL−1 TNT was obtained, which is five times lower than that obtained with a previously described colloidal gold-based LFIA developed employing the same immunoreagents. The dynamic range of the assay extended up to 5μgmL−1 TNT and recoveries ranging from 97% to 111% were obtained in the analysis of real samples (post blast residues obtained from controlled explosion).

Polygermole Nanoaggregate Chemical Sensor for TNT: Enhancement of Photoluminescence Efficiency by Aggregation-Induced Emission

New photoluminescent and nanoscale polygermole nanoaggregates for the detection of 2,4,6-trinitrotoluene (TNT) were developed by using aggregation-induced emission property. Polygermole nanoaggregates displaying diameter of 40 nm exhibited that photoluminescence (PL) intensity of emission band was increased about 730% when the water fraction was increased to 90% by volume. Relative PL efficiency of polygermole nanoaggregates was exponentially increased to the percent of water fraction and particle diameter was dependent on solvent composition. Particle size of polygermole nanoaggregates was tuned by controlling the water fraction by volume. PL intensity of polygermole nanoaggregates was not changed over a month. This indicated that polygermole nanoaggregates showed neither further aggregation nor degradation. Detection of TNT was achieved from the measuring of quenching PL of polygermole nanoaggregates by adding the TNT A linear Stern-Volmer relationship was observed for the detection of TNT.

Rapid method for qualitative detection of in environmental samples.

A gel-based immunoassay that can be used for the detection of 2,4,6-trinitrotoluene (TNT) in water samples was developed. Four polyclonal antibodies were generated in chickens using TNT derivatives. The assay was based on the immunoaffinity preconcentration and immuno-enzyme analysis of TNT in the gel. The results of the assay, assessed by color development, were evaluated visually and also by using a flatbed scanner and subsequent digital processing of the scanned gel. The most sensitive color mode, parameter S (saturation, HSB mode), was used for the immunoassay optimization and evaluation of the results. The immunoassays with the best parameters were optimized and characterized. A cut-off level of 5 µg TNT L-1 was reached for water samples. It was shown that tap and environmental water samples could be analyzed directly, without sample preparation and dilution. The developed test is acceptable for use in an on-site field test to provide rapid (about 15 min for six samples), qualitative and reliable results for making environmental decisions such as identifying "hot spots", monitoring of military and terrorist activities, and selecting of site samples for laboratory analysis.

Development and comparison of two immunoassays for the detection of 2,4,6-trinitrotoluene (TNT) based on surface plasmon resonance

This paper describes the development and comparison of two immunoassays for the detection of 2,4,6-trinitrotoluene (TNT) based on competitive inhibition. Two polyclonal antibodies were used in the immunoassay; one was prepared from 2,4,6-trinitrophenol–bovine serum albumin conjugate (anti-TNP-BSA Ab, goat IgG) and another from 2,4,6-trinitrophenyl–keyhole limpet hemocyanine conjugate (anti-TNPh-KLH Ab, rabbit IgG). A solid-phase immunoassay that consisted of physically immobilized TNP-BSA conjugate was allowed to interact with these antibodies and the resonance angle changes due to the biomolecular interactions were monitored by surface plasmon resonance (SPR). The quantification of TNT was based on the change in the resonance angle shift for binding of antibodies with a TNP-BSA conjugate, which occurred in the presence of TNT in solution. Both antibodies showed a high degree of affinity for TNT and varying degrees of cross-reactivity to the related nitroaromatic derivative compounds, such as 2,4-dinitrotoluene (DNT), 1,3-dinitrobenzene (DNB), 2-amino-4,6-dintitrotoluene (2A-4,6-DNT), 4-amino-2,6-dinitrotoluene (4A-2,6-DNT) and TNP. The anti-TNPh-KLH Ab prepared in our laboratory showed a detection limit of 0.006 ng/ml (6 ppt), which was comparable to or even better than the detection limit (0.095 ng/ml or 95 ppt) of a commercially available anti-TNP-BSA Ab for detection of TNT. A pepsin solution prepared with a glycine–HCl buffer (pH 2.0) was used for regeneration of the sensor surface. The duration for a single immunocycle was ∼19 and ∼13 min for anti-TNP-BSA Ab and anti-TNPh-KLH Ab immunosystems, respectively. The proposed immunoassay is simple and possesses good analytical characteristics for quantification of TNT.

Surface plasmon resonance immunosensor for highly sensitive detection of 2,4,6-trinitrotoluene

We have examined the sensing characteristics of a surface plasmon resonance (SPR) immunoassay for the detection of 2,4,6-trinitrotoluene (TNT) using an immunoreaction between 2,4,6-trinitrophenol–ovalbumin (TNP–OVA) conjugate and anti-2,4,6-trinitrophenol antibody (anti-TNP antibody). TNP–OVA conjugate was attached to a SPR-gold sensing surface by means of physical immobilization, which undergoes binding interaction with anti-TNP antibody. Both the immobilization and binding processes were studied from a change in the SPR-resonance angle. The quantification of TNT is based on the principle of indirect competitive immunoassay, in which the immunoreaction between the TNP–OVA conjugate and anti-TNP antibody was inhibited in the presence of free TNT in solution. The decrease in the resonance angle shift is proportional to an increase in concentration of TNT used for incubation. The immunoassay exhibited excellent sensitivity for the detection of TNT in the concentration range from 0.09 to 1000 ng/ml with good stability and reproducibility. The immunosensor developed could detect TNT as low as 0.09 ng/ml, within a response time of ∼22 min. The sensor surface was regenerated by a brief flow of pepsin solution, which disrupts the antigen–antibody complex without destroying the conjugate biofilm. Cross-reactivity of the SPR sensor to some structurally related nitroaromatic derivative and the detection of TNT in the presence of these nitroaromatic compounds were investigated. The cross-reactivity of the SPR sensor to 2,4-dinitrotoluene (2,4-DNT), 1,3-dinitrobenzene (1,3-DNB), 2-amino-4,6-dinitrotoluene (2A-4,6-DNT) and 4-amino-2,6-dinitrotoluene (4A-2,6-DNT) were very low (≤1.1%). The analytical characteristics of the proposed immunosensor are highly promising for the development of new field-portable sensors for on-site detection of landmines.