Attogram Sensing of Trinitrotoluene with a Self-Assembled Molecular Gelator

There is an ongoing need for explosive detection strategies to uncover threats to human security including illegal transport and terrorist activities. The widespread military use of the explosive trinitrotoluene (TNT) for landmines poses another particular threat to human health in the form of contamination of the surrounding environment and groundwater. The detection of explosives, particularly at low picogram levels, by using a molecular sensor is seen as an important challenge. Herein, we report on the use of a fluorescent metal-organic framework hydrogel that exhibits a higher detection capability for TNT in the gel state compared with that in the solution state. A portable sensor prepared from filter paper coated by the hydrogel was able to detect TNT at the picogram level with a detection limit of 1.82 ppt (parts per trillon). Our results present a simple and new means to provide selective detection of TNT on a surface or in aqueous solution, as afforded by the unique molecular packing through the metal-organic framework structure in the gel formation and the associated photophysical properties. Furthermore, the rheological properties of the MOF-based gel were similar to those of a typical hydrogel.

Simultaneous detection and quantification of explosives by a modified hollow cathode discharge ion source

PurposeSmart biosensors that can perform sensitive and selective monitoring of target analytes are tremendously valuable for trinitrotoluene (TNT) explosive detection. In this research, the pre-developed sensor was integrated with biological receptors in which they enhanced the sensitivity of the sensor. This is due to conjugated polydiacetylene onto a peptide-based molecular recognition element (Trp-His-Trp) for TNT molecules in graphene field-effect transistors (GR-FETs) as biosensor that is capable of responding to the presence of a TNT target with a colorimetric response. The authors confirmed the efficacy of the receptor while being attached to polydiacetylene (PDA) by observing the binding ability between the Trp-His-Trp and TNT to alter the electronic band structure of the PDA conjugated backbones. The purpose of this paper is to demonstrate a modular system capable of transducing small-molecule TNT binding into a detectable signal. The details of the real-time and selective TNT biosensor have been reported.Design/methodology/approachFollowing an introduction, this paper describes the way of fabrication GR-FETs with conventional photolithography techniques and the other processes, which is functionalized by the TNT peptide receptors. The authors first determined the essential TNT recognition elements from UV-visible spectrophotometry spectroscopy for PDA sensor unit fabrication. In particular, the blue percentage and the chromic response were used to characterize the polymerization parameter of the conjugatedpbackbone. A continuous-flow trace vapor source of nitroaromatics (two, four, six-TNT) was designed and evaluated in terms of temperature dependence. The TNT concentration was measured by liquid/gas extraction in acetonitrile using bubbling sequence. The sensor test is performed using a four-point probe and semiconductor analyzer. Finally, brief conclusions are drawn.FindingsBecause of their unique optical and stimuli-response properties, the polydiacetylene and peptide-based platforms have been explored as an alternative to complex mechanical and electrical sensing systems. Therefore, the authors have used GR-FETs with biological receptor-PDAs as a biosensor for achieving high sensitivity and selectivity that can detect explosive substances such as TNT. The transport property changed compared to that of the field-effect transistors made by intrinsic graphene, that is, the Dirac point position moved from positive Vg to negative Vg, indicating the transition of graphene fromp-type ton-type after annealing in TNT, and when the device was tested from RT, the response of the device was found to increase linearly with increasing concentrations. Average shifting rate of the Dirac peak was obtained as 0.1-0.3 V/ppm. The resulting sensors exhibited at the limit ppm sensitivity toward TNT in real-time, with excellent selectivity over various similar aromatic compounds. The biological receptor coating may be useful for the development of sensitive and selective micro and nanoelectronic sensor devices for various other target analytes.Originality/valueThe detection of illegally transported explosives has become important as the global rise in terrorism subsequent to the events of September 11, 2001, and is at the forefront of current analytical problems. It is essential that a detection method has the selectivity to distinguish among compounds in a mixture of explosives. So, the authors are reporting a potential solution with the designing and manufacturing of electrochemical biosensor using polydiacetylene conjugated with peptide receptors coated on GR-FETs with the colorimetric response for real-time detection of TNT explosives specifically.

Electrochemical detection of trinitrotoluene in water samples based on a natural mineral attapulgite modified electrode

PurposeSmart sensors based on graphene field effect transistor (GFET) and biological receptors are regarded as a promising nanomaterial that could be the basis for future generation of low-power, faster, selective real-time monitoring of target analytes and smaller electronics. So, the purpose of this paper is to provide details of sensors based on selective nanocoatings by combining trinitrotoluene (TNT) receptors (Trp-His-Trp) bound to conjugated polydiacetylene polymers on a graphene channel in GFET for detecting explosives TNT.Design/methodology/approachFollowing an introduction, this paper describes the way of manufacturing of the GFET sensor by using investigation methods for transferring graphene sheet from Cu foil to target substrates, which is functionalized by the TNT peptide receptors, to offer a system which has the capability of answering the presence of related target molecules (TNT). Finally, brief conclusions are drawn.FindingsIn a word, shortly after graphene discovery, it has been explored with a variety of methods gradually. Because of its exceptional electrical properties (e.g. extremely high carrier mobility and capacity), electrochemical properties such as high electron transfer rate and structural properties, graphene has already showed great potential and success in chemical and biological sensing fields. Therefore, the authors used a biological receptor with a field effect transistor (FET) based on graphene to fabricate sensor for achieving high sensitivity and selectivity that can detect explosive substances such as TNT. The transport property changed compared to that of the FET made by intrinsic graphene, that is, the Dirac point position moved from positive Vg to negative Vg, indicating the transition of graphene from p-type to n-type after annealing in TNT, and the results show the bipolar property change of GFET with the TNT concentration and the possibility to develop a robust, easy-to-use and low-cost TNT detection method for performing a sensitive, reliable and semi-quantitative detection in a wide detection range.Originality/valueIn this timeframe of history, TNT is a common explosive used in both military and industrial settings. Its convenient handling properties and explosive strength make it a common choice in military operations and bioterrorism. TNT and other conventional explosives are the mainstays of terrorist bombs and the anti-personnel mines that kill or injure more than 15,000 people annually in war-torn countries. In large, open-air environments, such as airports, train stations and minefields, concentrations of these explosives can be vanishingly small – a few parts of TNT, for instance, per trillion parts of air. That can make it impossible for conventional bomb and mine detectors to detect the explosives and save lives. So, in this paper, the authors report a potential solution with design and manufacture of a GFET sensor based on a biological receptor for real-time detection of TNT explosives specifically.

The detection of explosives and explosive related compounds is a subject of importance in several areas including environmental health, de-mining efforts (land and sea) and security and defence against terrorist activity. The use of electrochemical methods is particularly attractive as many common explosives contain suitable chemical groups to be detected using electrochemical methods. The electrochemical detection of explosives and related compounds in solution using a virtual metal electrode array and differential pulse voltammetry was achieved. The multiple sets of voltammetric data were integrated using multivariate analysis and matched with known substances present in explosives. Seven explosive substances: 2,4-initrotoluene, 2,6-dinitrotoluene, 3,4-dinitrotoluene, 2-nitrotoluene , octogen (HMX), pentaerithrytol tetranitrate (PETN), trinitrotoluene (TNT) and cyclonite (RDX) and a taggant agent 2,3‐dimethyl‐2,3‐dinitrobutane (DMNB) were subjected to analysis using four solid electrodes, namely glassy carbon, silver, gold and platinum in saline aqueous solutions to mimic an aquatic environment. The results obtained in Differential Pulse Voltammetry (DPV) from the different experiments with each electrode were combined to produce a single voltammogram, which was subjected to chemometric analysis using Partial Least Squares (PLS) and Principle Component Analysis Non-Iterative Partial Least Squares (PCA-NIPALS). A combination of the electrochemical signals obtained together with the use of chemometric analysis made it possible to discriminate between explosives and their mixtures and also to quantitate their concentration in saline solutions. These combinations created a mathematical array, which clearly separates the explosives, even if the electrochemical information is buried or mixed with the electrode background noise.

Introduction The development of a portable, miniaturized and cheap microsystem based on TFBAR (thin-film bulk acoustic resonator) sensors for detection of explosive substances for anti-terrorism control in public or private places, appeared over the last years like a big challenge of our days. The research work focused on a microsystem consisting of an array of TFBAR sensors, each provided with a specific biochemical layer. TFBAR sensors were built on Si wafers and formed from two gold metal electrodes with a piezoelectric layer between them. The AlN piezoelectric layer allows resonator operation at high frequencies of 1-10 GHz and a high quality factor[1]. In this way, tiny mass shifts at low vapor concentrations in the ppb-ppt range can be detected and quantified by the resonance frequency (fR) shift. Mass detection of a vapor-explosive substance is performed according to an biomolecule immobilization algorithm, with the help of antibodies specifically prepared for each explosive substance. When explosive vapors come into contact with the TFBAR resonant sensor, they bind to the sensor antibodies causing the change of the resonance frequency. We focused in this paper on TNT (trinitrotoluene) detection. Design The TFBAR structure (Fig.1a) will be made from silicon on which a Si 3 N 4 membrane (0.6-1.0um thickness) will be patterned. The membrane will be the support for the deposition of the piezoelectric layer AlN of 1um between two metal electrodes (Cr-Au) with thicknesses of 80-100 nm. A Ti/Pt resistor has been design for heating a small cavity around the sensor with the purpose of enhancing the TNT vapour quantity (Fig1.b). The TNT explosive molecule will be reacting antibodies deposited on the gold surface changing the resonance frequency of the sensor To obtain a dense, uniform piezoelectric layer and high piezoelectric coefficients, we must resort to the physical methods of deposition of thin layers such as sputtering deposition. The thickness of the piezoelectric layer should be within the 0.6-1.2um range. A higher thickness would be favorable to increase the piezoelectric coefficients but will simultaneously lead to a decrease of the resonance frequency and implicitly to a decrease of sensor sensitivity [2]. The thickness of silicon nitride and metallic electrodes also influence the resonance frequency of the sensor in sense of decreasing the resonance frequency. Surface Functionalization The explosive substance for which the surface functionalization and deposition of biomaterial was trinitrotoluene (TNT). At present, there are different techniques for detecting traces of explosive substances[3]. The sensor for explosive substances must be sensitive, selective and easily used in field applications. The selectivity of the sensor was achieved by specific interaction between the sensor’s sensitive layer and the explosive analyte. TFBAR structure with a biolayer has been considered the best choice for explosive substances detection. A change in a measurable property, such as the mass, translated in the change of resonant frequency was then used to determine the interaction of TNT with sensor active area. A gold surface functionalization method has been developed and optimized for deposition of biomaterial consisting of anti-TNT antibodies through Protein A / G and was chosen for tests with the TNT antigen, the protein that bound most on anti-TNT antibodies to the surface. The most efficient immobilization of anti-TNT antibodies on the gold surfaces was made by a chemical linker:11-mercapto-undecanoic-acid (11-MUA, SAMs) and a biomolecular linker: G protein, since the antibody alone has no affinity to the metal electrode. Electrochemical impedance characterization showed that anti-TNT antibodies immobilization through Protein G resulted in greater gold surface isolation (with a 40 kΩ resistance compared to 17 kΩ obtained by Protein A). Obtained results of TNT concentrations, in the range of 50-1000 ppm, showed a saturation of the gold surface at 1000 ppm and further testing should be done to determine the detection limit of the device and of biofunctionalization method sensitivity to concentrations lower than 50 ppm. For 10 ng TNT molecules on the active sensor area of 200x200 um2, the resonance frequency shifts for 4.9 GHz to 4.75 GHz. The quality factor was found Q = 300. Results and Conclusions A new sensor based on MEMS technology associated with the fabrication of a thin piezoelectric layer which allows resonator operation at high frequencies of 1-10 GHz and with a high quality factor has been developed. The system consists of an array of TFBAR sensors, each provided with a specific biochemical layer. This MEMS system will operate on a GHz frequency band with a mass detection sensitivity directly proportional to the resonance frequency of the sensor. Bioimmobilization of anti-TNT antibodies was obtained through Protein G and after testing a readable shift of fR was reached. Further testing should be done in order to determine the detection limit of the device and also for other explosive substances such as RDX. Next to this work, XDX (trinitro-triazinano). NG (nitroglycerin) and HMTD (Hexamethylene triperoxide diamine) sensors will be developed following the same TFBAR structure and resonant frequency shift principle.

Trinitrotoluene (TNT) is a highly explosive nitroaromatic compound that is used for military and terrorist activities such as the development of improvised explosive devices (IEDs), landmines and is the main charge or explosive in most of the anti-personal and anti-vehicle mines. Different chemicals/ contaminants associated with TNT in soils near buried land mines comprise the microbial transformation products of TNT (2-amino-4,6-dinitrotoluene [2-Am-DNT] and 4-amino-2,6-dinitrotoluene [4-Am-DNT]), manufacturing impurities of TNT (2,4-DNT, 2,6- DNT, and 1,3-DNB), and TNT. Time, cost, and casualties associated with demining have necessitated the demand for improved detection techniques with reduced false positives by directly detecting the explosive material, rather than casing material of mines. Different analytical methods used to detect trace level of explosives in soil include ion mobility mass spectrometry, gas chromatography-mass spectrometry (GC-MS), and liquid chromatographymass spectrometry (LC-MS) that require samples to be collected from hazardous sites to laboratories. This is extremely unsafe, time consuming, involve large and expensive instrumentation cost and specially trained staff. Thus, detecting chemical signatures of these nitroaromatics in soil infected with these chemicals due to leaked TNT mines can provide location of landmines/ landmine prone zones to aide humanitarian demining process. This paper illustrates soil analysis for explosives and selected contaminants by Raman spectroscopy as a chemical, nondestructive, remote sensing method. As with advancement of Raman-based standoff detection techniques, fieldportable instruments and UAV deployable probes, this technique can be effectively employed in detecting buried landmines based on specific chemical signatures of target analyte. In this present study, TNT-based nitroaromatic was assessed in contaminated soil samples using Raman spectroscopy, where uncontaminated soil was used as background and matrix for spiking target contaminants at different concentrations.

This study describes the application of confocal Raman microscopy to the detection and identification of explosives and their precursors in situ on undyed natural and synthetic fibres and coloured textile specimens. Raman spectra were obtained from explosives particles trapped between the fibres of the specimens. The explosives pentaerythritol tetranitrate (PETN), trinitrotoluene (TNT), and ammonium nitrate as well as the explosives precursors hexamethylenetetraamine (HMTA) and pentaerythritol were used in this study. Raman spectra were collected from explosives particles with maximum dimensions in the range 5–10 µm. Despite the presence of spectral bands arising from the natural and synthetic polymers and dyed textiles, the explosive substances could be identified by their characteristic Raman bands. Furthermore, Raman spectra were obtained from explosives particles trapped between highly fluorescent clothing fibres. Raman spectra of the explosive and explosive precursor substances on dyed and undyed clothing substrates were readily obtained in situ within 90 s without sample preparation and with no alteration of the evidential material. Copyright © 2009 John Wiley & Sons, Ltd.

Detection of explosives in vapor phase by field asymmetric ion mobility spectrometry with dopant-assisted laser ionization

Military grade trinitrotoluene (TNT), manufactured by complex nitration and purification procedures [1], contains over 99% α-2,4,6-trinitrotoluene and trace amounts of precursors, isomers, and oxidation by-products. The detection and determination of TNT and other explosives by gas chromatography (GC) has been reported by a number of authors and summarized in a recent review [2]. Impurities in TNT have been identified by thin-layer chromatography [3], nuclear magnetic resonance [4], and GC [5–7]. The major impurities in commercial TNT were found to be 2,4-dinitrotoluene (DNT); 2,3,4-TNT; 2,3,5-TNT; and 2,4,5-TNT in reported concentrations of 0.1 to 0.4%, with traces of other DNT isomers detected. A novel method for characterizing TNT origins by means by variation in 13C/12C ratios has been reported [8].

Hardware from a commercial-off-the-shelf (COTS) ion mobility spectrometry (IMS) based explosive trace detector (ETD) has been interfaced to an AB/SCIEX API 2000 triple quadrupole mass spectrometer. To interface the COTS IMS based ETD to the API 2000, the faraday plate of the IMS instrument and the curtain plate of the mass spectrometer were removed from their respective systems and replaced by a custom faraday plate, which was fabricated with a hole for passing the ion beam to the mass spectrometer, and a custom interface flange, which was designed to attach the IMS instrument onto the mass spectrometer. Additionally, the mass spectrometer was modified to increase the electric field strength and decrease the pressure in the differentially pumped interface, causing a decrease in the effect of collisional focusing and permitting a mobility spectrum to be measured using the mass spectrometer. The utility of the COTS-ETD/API 2000 configuration for the characterization of the gas phase ion chemistry of COTS-ETD equipment was established by obtaining mass and tandem mass spectra in the continuous ion flow and selected mobility monitoring operating modes and by obtaining mass-selected ion mobility spectra for the explosive standard 2,4,6 trinitrotoluene (TNT). This analysis confirmed that the product ion for TNT is [TNT - H](-), the predominant collision-induced dissociation pathway for [TNT- H](-) is the loss of NO and NO(2), and the reduced mobility value for [TNT - H](-) is 1.54 cm(2)V(-1) s(-1). Moreover, this analysis was attained for sample amounts of 1 ng and with a resolving power of 37. The objective of the research is to advance the operational effectiveness of COTS IMS based ETD equipment by developing a platform that can facilitate the understanding of the ion chemistry intrinsic to the equipment.

In this paper, a textile terahertz reduced ground microstrip patch antenna for detection of trinitrotoluene (TNT) has been proposed. The proposed antenna is employing black denim as substrate having dielectric constant of e r = 1.6. The design and simulation of antenna has been carried out using CS T Microwave Studio 2014. The ground and patch of the proposed antenna has been designed using copper of thickness 0.05μm. It has been analyzed that the proposed antenna has impedance bandwidth of 247 GHz with an operating frequency range of 8.0481THz-8.3321THz with resonant frequency of 8.208 THz. It has been observed that the textile terahertz reduced ground microstrip patch antenna has gain of 7.359 dB and directivity of 7.002 dBi. The proposed antenna has minimal return loss of −65.89 dB at resonant frequency of 8.208 THz. The proposed antenna can be suitably employed for the detection of the TNT explosives and drugs.

Explosive and chemical threat detection by surface-enhanced Raman scattering: A review

Explosives are one of many hazardous waste problems of concern to the Department of Defense. Defective storage facilities or byproducts of weapons manufacture have led to contamination of soil and water with explosives. Most explosives are toxic, thus posing an ecological and human health hazard. The ability to do on-site or down-stream detection of explosives will be invaluable for site characterization and remediation by saving both time and money. The evanescent wave fiber optic biosensor that was developed at NRL has been modified for the detection of trinitrotoluene (TNT), by developing a competitive immunoassay on the surface of an optical probe. A fluorescently labelled analog of TNT, trinitrobenzenesulfonic acid (TNB), was used as the competitor. Enzyme-linked immunosorbent assays were performed to determine the best fluorescently labeled competitor available to be able to achieve high sensitivity in the fiber optic assay. For the competition assay, 7.5 ng/ml Cyanine 5-ethylenediamine-labelled TNB (Cy5-EDA-TNB) was exposed to an antibody-coated optical fiber generating specific signal above background that corresponds to the 100% or reference signal. Inhibition of this signal was observed in the presence of TNT with the percent inhibition proportional to the TNT concentration in the sample. Detection sensitivities in aqueous solutions containing 10 ng/ml TNT (8 ppb) have been achieved using this system.