Role of Metal Ions in the Destruction of TATP: Theoretical Considerations

Colorimetric optical nanosensors for trace explosive detection using metal nanoparticles: advances, pitfalls, and future perspective

Warfare threats and acts of terror are challenging situations encountered by defense agencies across the globe and are of growing concern to the general public, and security-minded policy makers. Detecting ultra-low quantities of explosive compounds in remote locations or under harsh conditions for anti-terror purposes as well as the environmental monitoring of residual or discarded explosives in soil, remains a major challenge. The use of metal nanoparticles (NPs) for trace explosive detection has drawn considerable interest in recent years. For nano-based explosive sensor devices to meet real-life operational demands, analytical parameters such as, long-shelf life, stability under harsh conditions, ease-of-use, high sensitivity, excellent selectivity, and rapid signal response must be met. Generally, the analytical performance of colorimetric-based nanosensor systems is strongly dependent on the surface properties of the nanomaterial used in the colorimetric assay. The size and shape properties of metal NPs, surface functionalisation efficiency, and assay fabrication methods, are factors that influence the efficacy of colorimetric explosive nanosensor systems. This review reports on the design and analytical performances of colorimetric explosive sensor systems using metal NPs as optical signal transducers. The challenges of trace explosive detection, advances in metal NP colorimetric explosive design, limitations of each methods, and possible strategies to mitigate the problems are discussed.

Recent Developments in the Field of Explosive Trace Detection

Explosive trace detection (ETD) technologies play a vital role in maintaining national security. ETD remains an active research area with many analytical techniques in operational use. This review details the latest advances in animal olfactory, ion mobility spectrometry (IMS), and Raman and colorimetric detection methods. Developments in optical, biological, electrochemical, mass, and thermal sensors are also covered in addition to the use of nanomaterials technology. Commercially available systems are presented as examples of current detection capabilities and as benchmarks for improvement. Attention is also drawn to recent collaborative projects involving government, academia, and industry to highlight the emergence of multimodal screening approaches and applications. The objective of the review is to provide a comprehensive overview of ETD by highlighting challenges in ETD and providing an understanding of the principles, advantages, and limitations of each technology and relating this to current systems.

Ultra-sensitive gas phase detection of 2,4,6-trinitrotoluene by non-covalently functionalized graphene field effect transistors

The high energy density (4.2 MJ kg-1) and low vapour pressure (7.2 × 10-9 atm) of chemical explosives such as TNT (2,4,6-trinitrotoluene) pose a grave security risk demanding immediate attention. Detection of such hazardous and highly challenging chemicals demands specific, ultra-sensitive and rapid detection platforms that can concomitantly transduce the signal as an electrical readout. Although chemo-sensitive strategies have been investigated, the majority of them are restricted to detecting TNT from solutions and are therefore not implementable in real-time, on-field situations. Addressing this demand, we report an ultra-sensitive (parts-per-billion) and rapid (∼40 s) detection platform for TNT based on non-covalently functionalized graphene field effect transistors (GFETs). This multi-parametric GFET detector exhibits a reliable and specific modulation in its Dirac point upon exposure to TNT in the vapour phase. The chemical specificity provided by 5-(4-hydroxyphenyl)-10,15,20-tri(p-tolyl) zinc porphyrin (ZnTTPOH) is synergistically combined with the high surface sensitivity of graphene through a non-covalent functionalization approach to realise p-doped GFETs (Zn-GFETs). Such a FET platform exhibits extremely sensitive shifts in Dirac point (ΔDP) that correlate with the number of nitro groups present in the analyte. Analytes with mono-, di-, and tri-nitro substituted aromatic molecules exhibit distinctly different ΔDP, leading to unprecedented specificity towards TNT. Additionally, the Dirac point of Zn-GFETs is invariant for common and potential interferons such as acetone and 2-propanol (perfume emulsifiers) thereby validating their practical applicability. Furthermore, the ΔDP is also manifested as changes in the contact potential of GFETs, indicating that sub-monolayer coverage of ZnTTPOH is sufficient to modulate the transfer characteristics of GFETs over an area 1000 times larger than the dopant dimensions. Specifically, ZnTTPOH-functionalized GFETs exhibit p-doped behaviour with positive ΔDP with respect to pristine GFETs. Such p-doped Zn-GFETs undergo selective charge-transfer mediated interactions with TNT resulting in enhanced electron withdrawal from Zn-GFETs. Thus the ΔDP shifts to a higher positive gate voltage leading to the dichotomous combination of the highest signal generation (1.2 × 1012 V mol-1) with ppb level molecular sensitivity. Significantly, the signal generated due to TNT is 105 times higher in magnitude compared to other potential interferons. The signal reliability is established in cross-sensitivity measurements carried out with a TNT-mDNB (1 : 10 molar ratio) mixture pointing to high specificity for immediate applications under atmospherically relevant conditions pertaining to homeland security and global safety.

Highly Networked Capsular Silica-Porphyrin Hybrid Nanostructures as Efficient Materials for Acetone Vapor Sensing

The development of novel functional nanomaterials is critically important for the further evolution of advanced chemical sensor technology. For this purpose, metalloporphyrins offer unique binding properties as host molecules that can be tailored at the synthetic level and potentially improved by incorporation into inorganic materials. In this work, we present a novel hybrid nanosystem based on a highly networked silica nanoarchitecture conjugated through covalent bonding to an organic functional molecule, a tetraphenylporphyrin derivative, and its metal complexes. The sensing properties of the new hybrid materials were studied using a nanomechanical membrane-type surface stress sensor (MSS) with acetone and nitric oxide as model analytes. This hybrid inorganic-organic MSS-based system exhibited excellent performance for acetone sensing at low operating temperatures (37 °C), making it available for diagnostic monitoring. The hybridization of an inorganic substrate of large surface area with organic molecules of various functionalities results in sub-ppm detection of acetone vapors. Acetone is an important metabolite in lipid metabolism and can also be present in industrial environments at deleterious levels. Therefore, we believe that the analysis system presented by our work represents an excellent opportunity for the development of a portable, easy-to-use device for monitoring local acetone levels.

Rapid degradation of cyclic peroxides by titanium and antimony chlorides

Rapid and safe degradation of a cyclic peroxide (TPTP) to relatively innocuous products.