Detection Of Buried Landmines Research Articles

Eco‐friendly and Efficient Synthesis of Water‐soluble MoS2 Quantum Dot Probe for Smart Explosive Sensors

AbstractThe rapid detection of buried landmines has become a crucial concern of global security owing to the advancement in terrorist attacks. Indeed, the development of smart materials for the rapid detection of explosives especially nitro‐explosives is the need of time. However, the sensitivity and selectivity of materials for the detection of nitro‐explosives are major hurdles due to their low vapour pressure at room temperature. Albeit, it could be resolved by the use of advanced functional nanomaterials bearing high surface area and excellent optoelectronic properties. In this context, the water‐soluble MoS2 quantum dots (QDs) are synthesized by an ultrafast eco‐friendly hot injection method and potentially used for the detection of nitro‐explosives. The detection of picric acid (PA), 2,4,6‐Trinitrotoluene (TNT) and various other nitroaromatic compounds is performed by fluorescent probe technique. Notably, MoS2 QDs have effectively detected picric acid and TNT exhibiting detection limits of 5.13 ppm and 43.93 ppm respectively in water via a photoinduced electron transfer mechanism. Real‐time analysis of picric acid employing a paper strip of MoS2 QD as a fluorescent probe clearly demonstrates MoS2 QDs′ potential for practical usage in explosive detection. This work is patented: Application No. 202121000715 (applied).

Performance upgrade of a microbial explosives’ sensor strain by screening a high throughput saturation library of a transcriptional regulator

We present a methodology for a high-throughput screening (HTS) of transcription factor libraries, based on bacterial cells and GFP fluorescence. The method is demonstrated on the Escherichia coli LysR-type transcriptional regulator YhaJ, a key element in 2,4-dinitrotuluene (DNT) detection by bacterial explosives’ sensor strains. Enhancing the performance characteristics of the YhaJ transcription factor is essential for future standoff detection of buried landmines. However, conventional directed evolution methods for modifying YhaJ are limited in scope, due to the vast sequence space and the absence of efficient screening methods to select optimal transcription factor mutants. To overcome this limitation, we have constructed a focused saturation library of ca. 6.4 × 107 yhaJ variants, and have screened over 70 % of its sequence space using fluorescence-activated cell sorting (FACS). Through this screening process, we have identified YhaJ mutants exhibiting superior fluorescence responses to DNT, which were then effectively transformed into a bioluminescence-based DNT detection system. The best modified DNT reporter strain demonstrated a 7-fold lower DNT detection threshold, a 45-fold increased signal intensity, and a 40 % shorter response time compared to the parental bioreporter. The FACS-based HTS approach presented here may hold a potential for future molecular enhancement of other sensing and catalytic bioreactions.

Introduction of quorum sensing elements into bacterial bioreporter circuits enhances explosives' detection capabilities.

A possible solution for the standoff detection of buried landmines is based on the use of microbial bioreporters, genetically engineered to emit a remotely detectable optical signal in response to trace amounts of explosives’ signature chemicals, mostly 2,4‐dinitrotoluene (DNT). Previously developed DNT sensor strains were based on the fusion of a DNT‐inducible gene promoter to a reporting element, either a fluorescent protein gene or a bacterial bioluminescence gene cassette. In the present study, a different approach was used: the DNT‐inducible promoter activates, in Escherichia coli, the quorum‐sensing luxI and luxR genes of Aliivibrio fischeri. N‐Acyl homoserine lactone (AHL), synthesized by LuxI, combines with LuxR and activates the bioluminescence reporter genes. The resulting bioreporter displayed a dose‐dependent luminescent signal in the presence of DNT. Performance of the sensor strain was further enhanced by manipulation of the sensing element (combining the E. coli DNT‐inducible azoR and yqjF gene promoters), by replacing the luminescence gene cassette of Photorhabdus luminescens luxCDABE with A. fischeri luxCDABEG, and by introducing two mutations, eutE and ygdD, into the host strain. DNT detection sensitivity of the final bioreporter was over 340‐fold higher than the original construct.

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.

UAV-Borne FMCW InSAR for Focusing Buried Objects

Antipersonnel mines are hidden weapons that are usually buried close to the surface and are triggered by a foot step of the victim. A sensor that is able to detect minimum metal mines is a ground penetrating synthetic aperture radar (GPSAR). In previous work, an unmanned aerial vehicle (UAV)-based GPSAR was developed and tested for the detection of buried landmines. The real topography was neglected and the interface between air and soil was assumed as a horizontal plane surface. Since the dielectric properties of the soil reduce the propagation velocity of the electromagnetic wave, the interface between air and soil has to be known precisely for subsurface focusing. Neglecting the surface profile has a negative impact on the image quality and prevents the detection of buried objects. In this letter, a novel two-step procedure is used to overcome this issue. In time-division multiplex mode, the radar transmits two frequency-modulated ramps in two different frequency bands. The data of the upper frequency band are used to generate a digital elevation model (DEM) through interferometry. The data of the lower frequency band are used for GPSAR focusing on the basis of the DEM. It is demonstrated that the GPSAR image quality is improved on nonideal planar surfaces and the probability of detection is increased.

Improving Detection of a Portable NQR System for Humanitarian Demining Using Machine Learning

This article presents an approach to enhance the detection of buried landmines by applying machine learning (ML) to signals from a nuclear quadrupole resonance (NQR) system. This custom-made, low-cost, and portable NQR system has been developed for deployment in humanitarian demining, where strong radio frequency (RF) interference and a low signal-to-noise ratio (SNR) are important challenges for accurate detection. To tackle these problems, we have applied and tested various ML techniques to NQR signals acquired by our system in laboratory experiments with the explosive Research Department X (RDX). Results suggest that ML methods can indeed improve the detection accuracy of the NQR device, and this is confirmed further using data from field trials with our device. Importantly, the trained classifiers can be implemented with our device’s field-programmable gate array (FPGA) architecture and can run with little time penalty compared with simpler but less-efficient fast Fourier transform (FFT)-based energy detection methods.

Sense and sensibility: of synthetic biology and the redesign of bioreporter circuits.

Sense and sensibility: of synthetic biology and the redesign of bioreporter circuits.

The Escherichia coli azoR gene promoter: A new sensing element for microbial biodetection of trace explosives

Abstract DNT (2,4-dinitrotoluene), a volatile impurity in military grade TNT-based explosives, is a potential tracer for the detection of buried landmines and other explosive devices. We have previously described DNT bioreporter strains, based on a fusion between the Escherichia coli yqjF gene promoter to either a bacterial luxCDABE luminescence gene cassette or to the green fluorescent protein gene gfp. We now present the azoR gene promoter, demonstrated to be strongly induced by DNT, as an alternative sensing element for this compound. An E. coli bioreporter strain harboring a plasmid-borne fusion of the azoR promoter region to Photorhabdus luminescens luxCDABE displayed stronger bioluminescent responses to DNT than the yqjF-based bioreporter. The azoR promoter was induced not directly by DNT but by its degradation products; the most potent inducer was 2,4,5-trihydroxytoluene (THT). This reaction was positively regulated by YhaJ, a member of the LysR family of transcriptional regulators, and was significantly amplified in a yhaK mutant. We also show that DNT degradation in E. coli involves glutathione, which plays a vital role in azoR gene promoter activation.

Detection of buried explosives with immobilized bacterial bioreporters.

The unchecked dispersal of antipersonnel landmines since the late 19th century has resulted in large areas contaminated with these explosive devices, creating a substantial worldwide humanitarian safety risk. The main obstacle to safe and effective landmine removal is the identification of their exact location, an activity that currently requires entry of personnel into the minefields; to date, there is no commercialized technology for an efficient stand-off detection of buried landmines. In this article, we describe the optimization of a microbial sensor strain, genetically engineered for the remote detection of 2,4,6-trinitrotoloune (TNT)-based mines. This bioreporter, designed to bioluminescence in response to minute concentrations of either TNT or 2,4-dinitotoluene (DNT), was immobilized in hydrogel beads and optimized for dispersion over the minefield. Following modifications of the hydrogel matrix in which the sensor bacteria are encapsulated, as well as their genetic reporting elements, these sensor bacteria sensitively detected buried 2,4-dinitrotoluene in laboratory experiments. Encapsulated in 1.5mm 2% alginate beads containing 1% polyacrylic acid, they also detected the location of a real metallic antipersonnel landmine under field conditions. To the best of our knowledge, this is the first report demonstrating the detection of a buried landmine with a luminescent microbial bioreporter.

Genome-wide gene-deletion screening identifies mutations that significantly enhance explosives vapor detection by a microbial sensor

Genetically engineered microbial biosensors, capable of detecting traces of explosives residues above buried military ordnance and emitting an optical signal in response, may potentially serve for the standoff detection of buried landmines. A promising candidate for such an application is a previously reported Escherichia coli-based reporter strain that employs the yqjF gene promoter as its sensing element; however, for this sensor to be able to detect actual landmines reliably, it was necessary for its detection sensitivity and signal intensity to be enhanced. In this study, a high-throughput approach was employed to screen the effects of individual gene deletions on yqjF activation by 2,4-dinitrotoluene (DNT). Several genes were identified, the deletion of which elicited a significant enhancement of yqjF induction by DNT. The most promising of these mutations were introduced into the sensor strain, individually or in pairs, yielding a considerable increase in signal intensity and a lowering of the detection threshold. A strain harboring two of the identified mutations, ygdD and eutE, appears to be the most sensitive microbial biosensor currently described for the detection of traces of landmine explosives.

Robust landmine detection from thermal image time series using Hough transform and rotationally invariant features

ABSTRACT Automated detection of buried anti-personnel landmines using remote sensing techniques is very important for clearing minefields without putting lives in danger. Although thermal infrared imaging is promising, it is far from applicable to the real world in its current state-of-the-art. The most serious problem is that experiments are generally held using sandboxes or levelled and cleared soil, but real fields are, at least partially, covered with plants. In this study, we present an algorithm for landmine detection that is robust enough to detect beyond the clutter caused by partial plant cover. The first part is a hypothesis generator based on circular Hough Transform applied to images that are filtered to enhance circular structures. The second part tests the candidate landmine coordinates using rotationally invariant features, including modified Histogram of Oriented Gaussians (HOG), over multiple images taken at different times after Wiener filtering to maximize signal-to-clutter ratio. The performances of various features and classifiers are compared. The overall performance of the algorithm is demonstrated on a dataset of real-world landmine images contaminated by simulated plants. Satisfactory results are obtained up to 40% equivalent plant coverage where more than 65% of the pixels are fully or partially covered by plants.

Bacterial bioreporters for standoff detection of buried landmines: molecular manipulations for performance enhancement

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Aerobic Transformation of 2,4-Dinitrotoluene by Escherichia coli and Its Implications for the Detection of Trace Explosives.

DNT (2,4-dinitrotoluene), a volatile impurity in military-grade 2,4,6-trinitrotoluene (TNT)-based explosives, is a potential tracer for the detection of buried landmines and other explosive devices. We have previously described an Escherichia coli bioreporter strain engineered to detect traces of DNT and have demonstrated that the yqjF gene promoter, the sensing element of this bioreporter, is induced not by DNT but by at least one of its transformation products. In the present study, we have characterized the initial stages of DNT biotransformation in E. coli, have identified the key metabolic products in this reductive pathway, and demonstrate that the main DNT metabolite that induces yqjF is 2,4,5-trihydroxytoluene. We further show that E. coli cannot utilize DNT as a sole carbon or nitrogen source and propose that this compound is metabolized in order to neutralize its toxicity to the cells.IMPORTANCE The information provided in this article sheds new light both on the microbial biodegradability of nitroaromatic compounds and on the metabolic capabilities of E. coli By doing so, it also clarifies the pathway leading to the previously unexplained induction of the E. coli yqjF gene by 2,4-dinitrotoluene, an impurity that accompanies 2,4,6-trinitrotoluene (TNT)-based explosives. Our improved understanding of these processes will serve to molecularly enhance the performance of a previously described microbial bioreporter of buried landmines and other explosive devices, in which the yqjF gene promoter serves as the sensing element.

The importance of tuning curves and two-tone tests in nonlinear acoustic landmine detection

During the 1990s through ∼2010, Jim Sabatier’s group (Univ. Mississippi and NCPA) had made significant progress in understanding airborne acoustic landmine detection. In particular, using their development of scanning laser Doppler vibrometry, plastic anti-tank landmines could be detected in soil along roadbeds. Research on the nonlinear acoustic detection of buried landmines by Dimitry Donskoy (Stevens Tech) lead to lumped element models of the target which included a nonlinear spring-like mechanism. Tom Muir studied seismic excitations. Sabatier and Korman suggested that the soil nonlinearity and the soil interaction with the flexural vibration of the top-plate of the landmine or drum-like simulant were both significant factors in nonlinear landmine detection. Nonlinear tuning curves of the soil vibration response vs. frequency (directly over the target) along with rich combination frequency generation in two-tone tests suggested that the vibration was similar to Paul Johnson’s group results on mesoscopic nonlinear elasticity found in geomaterials. Recent airborne acoustic nonlinear landmine detection experiments compare drum-like simulant tuning curves to results using a soil plate oscillator apparatus (two circular flanges sandwiching and clamping a thin circular elastic plate that supports a cylindrical level column of sand above the plate) to help model flexural mesoscopic nonlinear hysteretic behavior.

Laser vibration sensing at Fraunhofer IOSB: review and applications

Laser vibrometry based on coherent detection allows noncontact measurements of small-amplitude vibration characteristics of objects. This technique, commonly using the Doppler effect, offers high potential for short-range civil applications and for medium- or long-range applications in defense and security. Most commercially available laser Doppler vibrometers are for short ranges (up to a few tens of meters) and use a single beam from a low-power HeNe laser source (λ=633 nm). Medium- or long-range applications need higher laser output power, and thus, appropriate vibrometers typically operate at 1.5, 2, or 10.6 μm to meet the laser safety regulations. Spatially resolved vibrational information can be obtained from an object by using scanning laser vibrometers. To reduce measuring time and to measure transient object movements and vibrational mode structures of objects, several approaches to multibeam laser Doppler vibrometry have been developed, and some of them are already commercially available for short ranges. We focus on applications in the field of defense and security, such as target classification and identification, including camouflaged or partly concealed targets, and the detection of buried land mines. Examples of civil medium-range applications are also given.

Novel Imaging Radar Technology for Detection of Landmines and Other Unexploded Ordnance

The safe, reliable, and efficient detection and subsequent removal of buried landmines or other unexploded ordnance (UXO) still remains a challenge. According to Landmine Monitor (2015), almost 60 states suffer the threat of antipersonnel mine contamination, while the total extent of contaminated areas is likely to be thousands of square kilometers and the total number of threat objects may be well over 100 million. In contrast, total annual clearing rates are in the order of about 230,000 landmines and about 200 km2 for the year of 2014, as the number of new contaminations continues to grow. Although non-technical surveillance for the identification of contamination improves slowly, more progress is needed in the basic detection of UXO. Although many new technologies have been investigated the last 20 years, the classical ones like metal detectors and dogs in cooperation with humans operators are still the most commonly ones used today. Hence, the detection process for many scenarios is unacceptably slow and dangerous for the operators, as they are typically less than 1 m away from the threats. Hence, a sensor technology enabling a sufficient stand-off distance for operators and reliable detection at high area throughput is desirable. The following paper describes the physical background, the system design, and representative measurement results of our innovative radar approach to this problem.

Of Mice and Men [Turnstile

Presents information on the current state of the art in the detection of buried land mines and unexploded ordnance.

Detection of 2,4-dinitrotoluene and 2,4,6-trinitrotoluene by an Escherichia coli bioreporter: performance enhancement by directed evolution.

The use of bacterial bioreporters for the detection of buried landmines and other explosive devices has been promoted for over 25 years, and several bacterial sensor strains capable of detecting traces of either 2,4,6-trinitrotoluene (2,4,6-TNT) or 2,4-dinitrotoluene (2,4-DNT) have since been reported. In all cases, however, detection sensitivity failed to reach the levels required to reliably sense the minute concentrations of 2,4-DNT vapors expected to exist in the soil above buried landmines. Here, we report on the application of a directed evolution process to enhance the performance of a previously described E. coli-based bioreporter harboring a plasmid-borne genetic fusion between the yqjF gene promoter and either luxCDABE or gfp genes, generating bioluminescent or fluorescent signals, respectively, in the presence of either 2,4,6-TNT or its main "signature" compound, 2,4-DNT. We have performed four sequential rounds of random mutagenesis to the yqjF promoter region, yielding a fourth-generation sensor that displayed significantly improved 2,4-DNT detection characteristics compared to the wild-type and to previous generations. Luminescence intensity in the presence of aqueous 2,4-DNT increased over 3000-fold, response ratios were improved over 50-fold, detection threshold was reduced by 75 %, and response time was cut down to half. These features were manifested also upon exposure to 2,4-DNT vapors or to 2,4-DNT and 2,4,6-TNT buried in sand. An analysis of the point mutations accumulated in the course of this process indicated that the major contributors to these effects were manipulations of the -35 element of the yqjF gene promoter.

Development and Performance of an Ultrawideband Stepped-Frequency Radar for Landmine and Improvised Explosive Device (IED) Detection

Under support from the Army Research Laboratory’s Partnerships in Research Transition program, a stepped-frequency radar (SFR) is currently under development, which allows for manipulation of the radiated spectrum while still maintaining an effective ultra-wide bandwidth. The SFR is a vehicle-mounted forward-looking ground-penetrating radar designed for high-resolution detection of buried landmines and improvised explosive devices. The SFR can be configured to precisely excise prohibited or interfering frequency bands and also possesses frequency-hopping capabilities. This paper discusses the expected performance features of the SFR as derived from laboratory testing and characterization. Ghosts and artifacts appearing in the range profile arise from gaps in the operating band when the system is configured to omit specific frequencies. An analysis of these effects is discussed and our current solution is presented. Future prospects for the SFR are also discussed, including data collection campaigns at the Army’s Adelphi Laboratory Center and the Countermine Test Site.

Topographic Correction of Elevated GPR

It is often advantageous to acquire ground-penetrating radar (GPR) measurements from antennas that are elevated above the ground surface, for example, in the detection of buried landmines. In this case, the electromagnetic (EM) wave always propagates through ground surface between the GPR and targets. Therefore, the variations of ground surface elevation will affect the propagation ray of EM wave. Accordingly, the subsurface target imaging will be deformed, especially the imaging in the horizontal slice, by the variations in elevation. In this study, we propose a fast method of topographic correction, which is based on the velocity model estimated by the elevated common midpoint GPR itself, to compensate the effects of variations in elevation. The method substitutes the air layer between the antenna and the ground with the soil layer by shifting the propagation time. The method was tested using experiment data acquired over a sloping ground surface under which a landmine model was shallowly buried. The result showed that the quality of target imaging was improved in slices, especially in the horizontal slice.