Sensors--an effective approach for the detection of explosives

Using Au@nano-C60 nanocomposite as an enhanced sensing platform in modeling a TNT aptasensor

Based on the unique characteristics of the combination of fullerene and gold nanoparticles, we successfully designed a new and facile nanocomposite (Au@nano-C60) to fabricate an aptasensor for the ultra-sensitive and selective detection of TNT. The gold nanoparticles decorated fullerene onto a glassy carbon electrode was prepared using an electrochemical method by the in situ generation of Au nanoparticles onto the surface of the glassy carbon electrode modified with activated fullerene. Successively, the NH₂-Apt as a receptor molecule of 2,4,6-Trinitrotoluen was covalently attached onto the modified electrode surface with the resultant nanocomposite. With the addition of the target onto the aptasensor surface and the formation of target/Apt complex, a linear response was obtained from 0.50 fM to 5 μM as well as a limit of detection down to 0.17 fM. The proposed aptasensor shows a wider linear response range and lower limit of detection for the specific detection of 2,4,6-Trinitrotoluen. This newly developed strategy will pave the way to partly meet the requirements in the field of homeland security and public safety.

Pendant chain engineering to fine-tune the nanomorphologies and solid state luminescence of naphthalimide AIEEgens: application to phenolic nitro-explosive detection in water

Strategically, a series of five angular "V" shaped naphthalimide AIEEgens with varying pendant chains (butyl, hexyl, octyl, cyclohexyl and methylcyclohexyl) have been synthesized to fine-tune their nanomorphological and photophysical properties. With similar aromatic cores and electronic states, unexpected tuning of the condensed state emission colors and nanomorphologies (reproducible on any kind of surface) of naphthalimides has been achieved for the first time simply by varying their side chains. Conclusive analysis by various spectroscopic techniques (SC-XRD, powder-XRD, DLS, FESEM) and DFT computational studies confirmed the full control of the pendant chain (in terms of bulkiness around the naphthalimide core, which restricts the ease of intermolecular π-π interactions) over the nanoaggregate morphology and solid state emissive properties of the AIEEgens; this can be rationalized to all aggregation-prone systems. These comprehensive studies establish a conceptually unique yet simple and effective method to precisely tune the nanomorphologies and the emission colors of aggregation-prone small organic molecules by judicious choice of the non-conjugated pendant chain. Thus, considering the prime role of the active layer nanomorphology in all organic optoelectronic devices, this methodology may emerge as a promising tool to improve device performance. Among all the congeners, the hexyl chain-containing congener (HNQ) forms well-defined nanoribbons with smaller diameters (as confirmed from DLS: 166 nm and FESEM: 150 nm) and provides a larger surface area. Consequently, the HNQ-nanoribbons were employed as a fluorescent sensor for the discriminative detection of trinitrophenol (TNP) in pure aqueous media. FE-SEM images revealed that, upon gradual addition of TNP (10 nM to 100 μM), these nanoribbons undergo an aggregation/disaggregation process, forming non-fluorescent co-aggregates with TNP, and provide highly enhanced sensitivity compared to existing state-of-the-art on aggregation-prone systems. Fluorescence titration studies confirmed that HNQ can detect the presence of TNP as low as 16.8 ppb and can serve as a cost-effective portable device incorporated with UV-light for on-site visual detection of TNP, even in the presence of potentially competing nitroaromatic compounds.

A turn-off fluorescence sensor for insensitive munition using anthraquinone-appended oxacalix[4]arene and its computational studies

Herein, a fluorescent oxacalix[4]arene-based receptor, DAQTNOC(5,17-di(N-(9,10-dioxo-9,10-dihydroanthracen-1-yl)acetamide) tetranitrooxacalix[4]arene), was described for the specific recognition of N-methyl-p-nitroaniline (MNA).

Development of luminescent sensors based on transition metal complexes for the detection of nitroexplosives

The detection of nitro explosives by transition metal complexes/metallosupramolecules with their designs and sensing mechanisms are comprehensively reviewed.

A supramolecular Tröger's base derived coordination zinc polymer for fluorescent sensing of phenolic-nitroaromatic explosives in water

A Tröger’s base functionalized luminescent nanoscale Zn(II) coordination polymer (TB-Zn-CP) is synthesized and used as selective fluorescence sensor for phenolic nitroaromatics in water.

A V-Shaped 4-amino-1,8-napthalimide derived tetracarboxylic acid linker (L; bis-[N-(1,3-benzenedicarboxylic acid)]-9,18-methano-1,8-naphthalimide-[b,f][1,5]diazocine) comprising the Tröger's base (TB) structural motif was rationally designed and synthesised to access a nitrogen-rich fluorescent supramolecular coordination polymer. By adopting the straight forward precipitation method, a new luminescent nanoscale Zn(ii) coordination polymer (TB-Zn-CP) was synthesized in quantitative yield using Zn(OAc)₂·2H₂O and tetraacid linker L (1 : 0.5) in DMF at room temperature. The phase-purity of as-synthesised TB-Zn-CP was confirmed by X-ray powder diffraction analysis, infra-red spectroscopy, and elemental analysis. Thermogravimetric analysis suggests that TB-Zn-CP is thermally stable up to 330 °C and the morphological features of TB-Zn-CP was analysed by SEM and AFM techniques. The N₂ adsorption isotherm of thermally activated TB-Zn-CP at 77 K revealed a type-II reversible adsorption isotherm and the calculated Brunauer–Emmett–Teller (BET) surface area was found to be 72 m² g^–1. Furthermore, TB-Zn-CP displayed an excellent CO₂ uptake capacity of 76 mg g^–1 at 273 K and good adsorption selectivity for CO₂ over N₂ and H₂. The aqueous suspension of as-synthesized TB-Zn-CP showed strong green fluorescence (λ_max = 520 nm) characteristics due to the internal-charge transfer (ICT) transition and was used as a fluorescent sensor for the discriminative sensing of nitroaromatic explosives. The aqueous suspension of TB-Zn-CP showed the largest quenching responses with high selectivity for phenolic-nitroaromatics (4-NP, 2,4-DNP and PA) even in the concurrent presence of other potentially competing nitroaromatic analytes. The fluorescence titration studies also provide evidence that TB-Zn-CP detects picric acid as low as the parts per billion (26.3 ppb) range. Furthermore, the observed fluorescence quenching responses of TB-Zn-CP towards picric acid were highly reversible. The highly selective fluorescence quenching responses including the reversible detection efficiency make the nanoscale coordination polymer TB-Zn-CP a potential material for the discriminative fluorescent sensing of nitroaromatic explosives.

Nitroaromatic explosives detection using electrochemically exfoliated graphene

Detection of nitroaromatic explosives is of paramount importance from security point of view. Graphene sheets obtained from the electrochemical anodic exfoliation of graphite foil in different electrolytes (LiClO₄ and Na₂SO₄) were compared and tested as electrode material for the electrochemical detection of 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT) in seawater. Voltammetry analysis demonstrated the superior electrochemical performance of graphene produced in LiClO₄, resulting in higher sensitivity and linearity for the explosives detection and lower limit of detection (LOD) compared to the graphene obtained in Na₂SO₄. We attribute this to the presence of oxygen functionalities onto the graphene material obtained in LiClO₄ which enable charge electrostatic interactions with the –NO₂ groups of the analyte, in addition to π-π stacking interactions with the aromatic moiety. Research findings obtained from this study would assist in the development of portable devices for the on-site detection of nitroaromatic explosives.

Demining Dogs in Colombia - A Review of Operational Challenges, Chemical Perspectives, and Practical Implications

Within the framework of an internal armed conflict in Colombia, the use of antipersonnel mines by revolutionary armed forces represents a strategic factor for these groups. Antipersonnel mines are used by these revolutionary forces as a mean to hinder the advancement of the national armed forces in the recovery of territory and to protect tactical natural resources and illegal economies within a given area. These antipersonnel mines and improvised explosive devices (IEDs) are not of industrial manufacturing, and have a variety of activating mechanisms as well as non-metal materials which make them difficult for successful detection. The Colombian experience strongly represents the current need for advanced research and development of effective field operations within its affected territory. Current efforts are focused on a more operational demining perspective in coca cultivation sites in charge of mobile squadrons of eradication (EMCAR) from the National Police of Colombia working towards a future humanitarian demining upon an eventual peace process. The objectives of this review are not only to highlight already existing mine detection methods, but present a special emphasis on the role of mine detection canine teams in the context of this humanitarian issue in Colombia. This review seeks to bring together a description of chemical interactions of the environment with respect to landmine odor signatures, as well as mine detection dog operational perspectives for this specific detection task. The aim is to highlight that given the limited knowledge on the subject, there is a research gap that needs to be attended in order to efficiently establish optimal operating conditions for the reliable performance of mine detection dogs in Colombian demining field applications.

Olfactory Sensitivity in Mammalian Species

Olfaction enables most mammalian species to detect and discriminate vast numbers of chemical structures called odorants and pheromones. The perception of such chemical compounds is mediated via two major olfactory systems, the main olfactory system and the vomeronasal system, as well as minor systems, such as the septal organ and the Grueneberg ganglion. Distinct differences exist not only among species but also among individuals in terms of their olfactory sensitivity; however, little is known about the mechanisms that determine these differences. In research on the olfactory sensitivity of mammals, scientists thus depend in most cases on behavioral testing. In this article, we reviewed scientific studies performed on various mammalian species using different methodologies and target chemical substances. Human and non-human primates as well as rodents and dogs are the most frequently studied species. Olfactory threshold studies on other species do not exist with the exception of domestic pigs. Olfactory testing performed on seals, elephants, and bats focused more on discriminative abilities than on sensitivity. An overview of olfactory sensitivity studies as well as olfactory detection ability in most studied mammalian species is presented here, focusing on comparable olfactory detection thresholds. The basics of olfactory perception and olfactory sensitivity factors are also described.

Essential Limitations of the Standard THz TDS Method for Substance Detection and Identification and a Way of Overcoming Them

Low efficiency of the standard THz TDS method of the detection and identification of substances based on a comparison of the spectrum for the signal under investigation with a standard signal spectrum is demonstrated using the physical experiments conducted under real conditions with a thick paper bag as well as with Si-based semiconductors under laboratory conditions. In fact, standard THz spectroscopy leads to false detection of hazardous substances in neutral samples, which do not contain them. This disadvantage of the THz TDS method can be overcome by using time-dependent THz pulse spectrum analysis. For a quality assessment of the standard substance spectral features presence in the signal under analysis, one may use time-dependent integral correlation criteria.

Detection of Explosives Using Differential Laser-Induced Perturbation Spectroscopy with a Raman-based Probe

Explosives detection is carried out with a novel spectral analysis technique referred to as differential laser-induced perturbation spectroscopy (DLIPS) on thin films of TNT, RDX, HMX, and PETN. The utility of Raman spectroscopy for detection of explosives is enhanced by inducing deep ultraviolet laser perturbation on molecular structures in combination with a differential Raman sensing scheme. Principal components analysis (PCA) is used to quantify the DLIPS method as benchmarked against a traditional Raman scattering probe, and the related photo-induced effects on the molecular structure of the targeted explosives are discussed in detail. Finally, unique detection is observed with TNT samples deposited on commonly available background substrates of nylon and polyester. Overall, the data support DLIPS as a noninvasive method that is promising for screening explosives in real-world environments and backgrounds.

Fiber-optic detection of nitroaromatic explosives with solution-processable triazatruxene-based hyperbranched conjugated polymer nanoparticles

Solution-processable triazatruxene-based hyperbranched conjugated polymer nanoparticles have been developed as homogeneous, transparent fluorescent films coated on glass substrates and on optic-fiber tips for the detection of TNT vapor.

Fluorescence tuning of Zn(ii)-based metallo-supramolecular coordination polymers and their application for picric acid detection

A series of metallo-supramolecular coordination polymers displayed strong and tunable visible luminescent emission and possessed the capability for detection of picric acid (PA) with high sensitivity and selectivity.

An effective method for substance detection using the broad spectrum THz signal with a "terahertz nose"

We propose an effective method for the detection and identification of dangerous substances by using the broadband THz pulse. This pulse excites, for example, many vibrational or rotational energy levels of molecules simultaneously. By analyzing the time-dependent spectrum of the THz pulse transmitted through or reflected from a substance, we follow the average response spectrum dynamics. Comparing the absorption and emission spectrum dynamics of a substance under analysis with the corresponding data for a standard substance, one can detect and identify the substance under real conditions taking into account the influence of packing material, water vapor and substance surface. For quality assessment of the standard substance detection in the signal under analysis, we propose time-dependent integral correlation criteria. Restrictions of usually used detection and identification methods, based on a comparison between the absorption frequencies of a substance under analysis and a standard substance, are demonstrated using a physical experiment with paper napkins.

Ultratrace Detection of Nitroaromatics: Picric Acid Responsive Aggregation/Disaggregation of Self-Assembled p-Terphenylbenzimidazolium-Based Molecular Baskets

1-(p-Terphenyl)-benzimidazolium (TRIPOD-TP) molecules undergo self-assembly to form rodlike structures in aqueous medium, as shown by field-emission scanning electron microscopy, transmission electron microscopy, and dynamic light scattering studies. Upon gradual addition of picric acid (PA), these aggregates undergo an aggregation/disaggregation process to complex morphological structures (10(-12)-10(-10) M PA) and spherical aggregates (10(-9)-10(-8) M PA). These spherical aggregates undergo further dissolution to well-dispersed spheres between 10(-7)-10(-6) M PA. During fluorescence studies, these aggregates demonstrate superamplified fluorescence quenching (>97%) in the presence of 10(-5) to 0.2 equiv of the probe concentration, an unprecedented process with PA. The lowest detection limits by solution of TRIPOD-TP are 5 × 10(-13) PA, 50 × 10(-12) M 2,4-dinitrophenol, 200 × 10(-12) M 2,4,6-trinitrotoluene, and 1 nM 1-chloro-2,4-dinitrobenzene. Paper strips dipped in the solution of TRIPOD-TP demonstrate quantitative fluorescence quenching between 10(-17) and 10(-6) M PA using front-surface steady state studies and can measure as low as 2.29 × 10(-20) g/cm(2) PA.

Self-assembled discrete molecules for sensing nitroaromatics

Efficient sensing of trace amount nitroaromatic (NAC) explosives has become a major research focus in recent time due to concerns over national security as well as their role as environment pollutants. NO2 -containing electron-deficient aromatic compounds, such as picric acid (PA), trinitrotoluene (TNT), and dinitrotoluene (DNT), are the common constituents of many commercially available chemical explosives. In this article, we have summarized our recent developments on the rational design of electron-rich self-assembled discrete molecular sensors and their efficacy in sensing nitroaromatics both in solution as well as in vapor phase. Several π-electron-rich fluorescent metallacycles (squares, rectangles, and tweezers/pincers) and metallacages (trigonal and tetragonal prisms) have been synthesized by means of metal-ligand coordination-bonding interactions, with enough internal space to accommodate electron-deficient nitroaromatics at the molecular level by multiple supramolecular interactions. Such interactions subsequently result in the detectable fluorescence quenching of sensors even in the presence of trace quantities of nitroaromatics. The fascinating sensing characteristics of molecular architectures discussed in this article may enable future development of improved sensors for nitroaromatic explosives.

A triphenylene-based conjugated microporous polymer: construction, gas adsorption, and fluorescence detection properties

A conjugated microporous triphenylene-based polymer has been synthesized and characterized with high CO₂ and H₂ adsorption as well as fluorescent response to nitrobenzene.

PET governed fluorescence “Turn ON” BODIPY probe for selective detection of picric acid

The non-fluorescent meso diaminophenyl 1,3,5,7-tetramethyl BODIPY dye has been investigated and employed for picric acid sensing in a constructive way by regenerating its fluorescence through PET hindrance.

The mechanism of 2,4,6-trinitrotoluene detection with amino acid-capped quantum dots: a density functional theory study

Both a Meisenheimer complex and deprotonated TNT are formed when TNT meets amino acid-capped quantum dots.

DFT and TD-DFT studies on the electronic and optical properties of explosive molecules adsorbed on boron nitride and graphene nano flakes

The binding affinity of explosive molecules with 2D BN flakes is higher than G flakes due to more charge transfer in the BN-explosive complexes.

Detection of nitroaromatic vapours with diketopyrrolopyrrole thin films: exploring the role of structural order and morphology on thin film properties and fluorescence quenching efficiency

Sensitive optical detection of nitroaromatic vapours with diketopyrrolopyrrole thin films is reported for the first time.

Fluorogenic displacement biosensors for PSA detection using antibody-functionalised quantum dot nanoparticles

Novel quantum dot conjugated immunosensors are presented for the accurate identification of seminal fluid in forensic casework.

π-Electron rich small molecule sensors for the recognition of nitroaromatics

In this review article we provide an overview of the recent developments made in small molecule-based turn-off fluorescent sensors for nitroaromatic explosives with special focus on organic and H-bonded supramolecular sensors.

Glucopyranosyl-1,4-dihydropyridine as a new fluorescent chemosensor for selective detection of 2,4,6-trinitrophenol

Glucopyranosyl-1,4-dihydropyridine (Glc-DHP) was synthesized as a new fluorescent chemosensor via cyclotrimerization of the β-amino acrylate in the presence of TiCl₄.

Nanoconfinement of pyrene in mesostructured silica nanoparticles for trace detection of TNT in the aqueous phase

This article describes the preparation of pyrene confined mesostructured silica nanoparticles for the trace detection of trinitrotoluene (TNT) in the aqueous phase. Pyrene confined mesostructured silica nanoparticles were prepared using a facile one-pot method where pyrene molecules were first encapsulated in the hydrophobic parts of cetyltrimethylammonium micelles and then silica polymerized around these micelles. The resulting hybrid particles have sizes of around 75 nm with fairly good size distribution. Also, they are highly dispersible and colloidally stable in water. More importantly, they exhibit bright and highly stable pyrene excimer emission. We demonstrated that excimer emission of the particles exhibits a rapid, sensitive and visual quenching response against TNT. The detection limit for TNT was determined to be 12 nM. Furthermore, excimer emission of pyrene shows significantly high selectivity for TNT.

Towards an electronic dog nose: surface plasmon resonance immunosensor for security and safety

This review describes an “electronic dog nose” based on a surface plasmon resonance (SPR) sensor and an antigen–antibody interaction for security and safety. We have concentrated on developing appropriate sensor surfaces for the SPR sensor for practical use. The review covers different surface fabrications, which all include variations of a self-assembled monolayer containing oligo(ethylene glycol), dendrimer, and hydrophilic polymer. We have carried out detection of explosives using the sensor surfaces. For the SPR sensor to detect explosives, the vapor or particles of the target substances have to be dissolved in a liquid. Therefore, we also review the development of sampling processes for explosives, and a protocol for the measurement of explosives on the SPR sensor in the field. Additionally, sensing elements, which have the potential to be applied for the electronic dog nose, are described.

Self-assembled monolayers of thiols adsorbed on Au/ZnO-functionalized silica nanosprings: photoelectron spectroscopy-analysis and detection of vaporized explosives

Self-assembled monolayers (SAMs) of thiols of L-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, DL-thioctic acid and 11-(1-pyrenyl)-1-undecathiol, which have been selected for their propensity to interact with vaporized explosives, have been attached from solution onto gold decorated ZnO-coated nanosprings. X-ray and ultraviolet photoelectron spectroscopies (XPS and UPS) have been used to investigate the surface electronic structure of the SAMs coated nanosprings. On the basis of XPS analysis, it has been determined that the packing densities of L-cysteine, 6-mercaptohexanol, 4-mercaptobenzoic acid, DL-thioctic acid and 11-(1-pyrenyl)-1-undecathiol on gold (zinc oxide) are 5.42 × 10(14) (2.83 × 10(14)), 3.26 × 10(14) (2.54 × 10(14)), 9.50 × 10(13), 2.55 × 10(14) (1.12 × 10(14)), and 5.23 × 10(13) molecules/cm(2), respectively. A single S 2p core level doublet is observed for 4-mercaptobenzoic acid and 11-(1-pyrenyl)-1-undecathiol, which is assigned to the S-Au bond. The S 2p core level for L-cysteine, 6-mercaptohexanol, and DL-thioctic acid consist of two doublets, where one is S-Au bond and the other is the S-Zn bond. Analysis of the C/S ratios agrees well with the stoichiometry of the respective thiols. UPS analysis shows that the hybridization of S 3p states and Au d-bands produces antibonding and bonding states, above and below the Au d-bands, which is characteristic of molecular chemisorption on Au nanoparticles. Gas sensors were constructed with thiolated nanosprings and their responsiveness to ammonium nitrate at 100-150 °C was tested. Nanosprings sensors functionalized with 4-mercaptobenzoic acid and 6-mercaptohexanol showed the strongest responses by a factor of 4 to 5 relative to the less responsive thiols. The response to ammonium nitrate can be correlated to the packing density and ordering of the SAMs.

Biosensors in forensic analysis. A review

Forensic analysis is an important branch of modern Analytical Chemistry with many legal and socially relevant implications. Biosensors can play an important role as efficient tools in this field considering their well known advantages of sensitivity, selectivity, easy functioning, affordability and capability of miniaturization and automation. This article reviews the latest advances in the use of biosensors for forensic analysis. The different methodologies for the transduction of the produced biological events are considered and the applications to forensic toxicological analysis, classified by the nature of the target analytes, as well as those related with chemical and biological weapons critically commented. The article provides several Tables where the more relevant analytical characteristics of the selected reported methods are gathered.