An enhanced colorimetric chemosensor for the detection of various nitro-explosives

The Combined Effect of Ambient Conditions and Diluting Salt on the Degradation of Picric Acid: An In Situ DRIFT Study

An unexpected promoting effect of KBr, used as a diluting salt, on the degradation of picric acid (PA) was observed during in situ diffuse reflectance infrared Fourier-transform (DRIFT) spectroscopy experiments performed here under accelerated ageing conditions-at 80 °C and under an inert or oxidative atmosphere. While the formation of potassium picrate was excluded, this promoting effect-which is undesired as it masks the possible effects of test conditions on the ageing process of the material-was assumed to favor a first step of the decomposition mechanism of PA, which involves the inter- or intramolecular transfer of hydrogen to the nitro group, and possibly proceeds up to the formation of an amino group. An alternative diluting salt, ZnSe, which is much less commonly used in infrared spectroscopy than KBr, was then proposed in order to avoid misleading interpretation of the results. ZnSe was found to act as a truly inert diluting salt, preventing the promoting effect of KBr. The much more chemically inert nature (towards PA) of ZnSe compared to KBr was also confirmed, at much higher temperatures than DRIFT experiments, by dynamic differential scanning calorimetry (DSC) runs carried out on pure PA (i.e., PA without salt) and PA/salt (ZnSe or KBr) solid mixtures.

Development of a gold nanoparticles-based colorimetric sensor for the indirect determination of ammonium dinitramide and tetryl

Ammonium dinitramide (ADN) is a strong, environmentally friendly oxidizer used in composite solid rocket propellants. As there is no reliable colorimetric sensor for ADN assay applicable to in-field screening, we developed a sensitive and practical sensing method to determine it in the presence of other explosives and possible interferents, based on the detection of nitrite formed from ADN degradation under UV light in a slightly alkaline (i.e. of lower alkalinity than needed to hydrolyze nitramines) solution by a nanoparticle-based colorimetric sensor. The ADN-derived nitrite formed a colored product via a Griess reaction using gold nanoparticles modified with 4-aminothiophenol (4-ATP-AuNPs) along with a coupling reagent N-(1-naphthyl)ethylene diamine (NED) for forming an azo dye. The method used for ADN detection could also be applied to tetryl samples at a different wavelength. The limit of detection (LOD) was 0.012 mg L^-1 for ADN and 0.615 mg L^-1 for tetryl. Interference effects of energetic materials like trinitrotoluene (TNT), hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and pentaerythritol tetranitrate (PETN) to ADN determination could be overcome. In addition, common soil ions did not adversely affect the nanosensor performance. The developed method was statistically validated against reference voltammetric, UV, and HPLC methods using t- and F- tests.

Colorimetric sensors and nanoprobes for characterizing antioxidant and energetic substances

The development of analytical techniques for antioxidant compounds is important, because antioxidants that can inactivate reactive species and radicals are health-beneficial compounds, also used in the preservation of food and protection of almost every kind of organic substance from oxidation. Energetic substances include explosives, pyrotechnics, propellants and fuels, and their determination at bulk/trace levels is important for the safety and well-being of modern societies exposed to various security threats. Most of the time, in field/on site detection of these important analytes necessitates the use of colorimetric sensors and probes enabling naked-eye detection, or low-cost and easy-to-use fluorometric sensors. The use of nanosensors brings important advantages to this field of analytical chemistry due to their various physico-chemical advantages of increased surface area, surface plasmon resonance absorption of noble metal nanoparticles, and superior enzyme-mimic catalytic properties. Thus, this critical review focuses on the design strategies for colorimetric sensors and nanoprobes in characterizing antioxidant and energetic substances. In this regard, the main themes and properties in optical sensor design are defined and classified. Nanomaterial-based optical sensors/probes are discussed with respect to their mechanisms of operation, namely formation and growth of noble metal nanoparticles, their aggregation and disaggregation, displacement of active constituents by complexation or electrostatic interaction, miscellaneous mechanisms, and the choice of metallic oxide nanoparticles taking part in such formulations.

Surface modified colloidal silica nanoparticles: Novel aspect for complete identification of explosive materials

Terrorism by means of explosives has become a crucial threat. Nanoparticles with distinctive properties can offer novel aspects for instant detection of explosive materials. Common explosives are organic compounds that contain nitro group (NO₂) along with carbon and hydrogen elements. This study demonstrates complete identification of nitramine explosives (RDX & HMX) using colloidal silica nanoparticles. Sustainable fabrication of colloidal silica was conducted via hydrothermal processing technique. Explosive identification involves a digestion of the tested material using strong acid. The digestion process results in the development of nitro group and corresponding formaldehyde segment. The identification of the nitro group was performed using colloidal silica nanoparticles functionalized with secondary amine to develop a characteristic dark blue colour. Simultaneous identification of formaldehyde segment was performed using colloidal silica functionalized with aromatic phenol to develop a red colour. This robust explosive detection technology can find wide applications on site where instant identification to assess potential threat is a crucial demand. Thanks to hydrothermal processing, sustainable fabrication and surface modification of colloidal silica particles can be obtained.