Pierre Montmeat

Ultra trace detection of explosives in air: Development of a portable fluorescent detector

This paper describes a system for the detection of nitroaromatic explosives consisting of a portable detector based on a specific fluorescent material. The developed sensor was able to perform an ultra trace detection of explosives, such as trinitrotoluene (TNT) or its derivate 2,4-dinitrotoluene (DNT), in ambient air or on objects tainted with explosives. In the presence of nitroaromatic vapors, the fluorescence of the material was found to decrease due to the adsorption of nitroaromatic molecules on its specific adsorption sites. The sensor exhibited a large sensitivity to TNT or DNT at their vapor pressures (respectively 6 and 148 ppbv) and the detection threshold was evaluated on a laboratory test setup and was found to be 0.75 ppbv for TNT. Moreover, the detector demonstrated no loss of performance in the presence of humidity or interfering compounds. All the tests led to the conclusion that the sensor fulfills the main requirements for the identification of suspect luggage, forensic analyses or battlefields clearing.

Metalloporphyrins as sensing material for quartz-crystal microbalance nitroaromatics sensors

Five octaethylporphyrins (OEP) and tetraphenylporphyrins (TPP): (OEP)InCl, (OEP)MnCl, (OEP)GaCl, (TPP)Pd, and (TPP)RhI have been deposited as sensitive coating onto quartz-crystal microbalances. The sensitivities of the resulting sensors have been measured with respect to 2,4-dinitrotrifluoromethoxybenzene vapors. When exposed to the nitroaromatic compound, a large and significative response is recorded for every tested porphyrin, the detection process being slightly reversible. Along with a good sensitivity, the sensors exhibit an excellent selectivity when common solvents are used as interfering vapors. Among all the studied derivatives, (OEP)MnCl appears as the most sensitive and selective coating.

Comparison of fluorescence and QCM technologies: Example of explosives detection with a π-conjugated thin film

A pi-conjugated compound was synthesized as a sensitive material for explosives detection. The detection of vapors of 2,4-dinitrotoluene was demonstrated with quartz crystal microbalance (QCM) and fluorescence transduction methods. The fluorescence intensity monitoring shows a higher sensitivity and selectivity than the monitoring of the QCM frequency. Both methods appear to be synergic when used simultaneously as the sensor helps to discriminate interferent vapors from nitroaromatics.

A simple thermodynamic approach to predict responses from polymer-coated quartz crystal microbalance sensors exposed to organic vapors

As of lately, the demand for developing artificial sensors with improved capabilities for the detection of explosives, toxics or drugs has increased. Ideally, sensor devices should provide high sensitivity and give a response that is specific to a given target molecule without being influenced by possible interfering molecules in the atmosphere. These properties strongly depend on the structure of the chemical compound used as a sensitive material. It is thus crucial to select the right compound and this step would be facilitated with the aid of predictive tools. The present investigations have been focused on a family of functionalized polysiloxane polymers deposited on a QCM device, producing only weak interactions compatible with reversible sensors. The quartz frequency variation at equilibrium has been linked to the partition coefficient that was evaluated using a thermodynamic description of the adsorption process. We have shown that the relative responses of two polymers can be directly determined from the Gibbs free enthalpy of mixing as determined from NMR measurements performed on neat liquid mixtures. An equivalence of this term-including both enthalpy and entropy contributions-to the energy interaction term calculated using Hansen solubility coefficients, has been demonstrated previously. These results constitute a basis for the development of a numerical program for calculating equilibrium sensor responses. For small molecules, the adsorption kinetics can be easily accounted for by a Fick diffusion coefficient estimated from the Van der Waals volume.

Ability of various materials to detect explosive vapors by fluorescent technologies: A comparative study ☆

For the development of fluorescent sensors, one of the key points is choosing the sensitive material. In this article, we aim at evaluating, under strictly identical experimental conditions, the performance of three materials for the detection of dinitrotoluene (a volatile marker of trinitrotoluene) through different parameters: response time, fluorescence intensity, sensitivity, reversibility, reaction after successive exposures and long-term stability. The results are discussed according to the nature of the sensitive materials. This first study rendered it possible to select a conjugated molecule as the best sensitive material for the development of a lab-made prototype. In a second part, the selectivity of this particular sensitive material was studied and its ability to detect TNT could be demonstrated.

Efficient Sensing of Explosives by Using Fluorescent Nonporous Films of Oligophenyleneethynylene Derivatives Thanks to Optimal Structure Orientation and Exciton Migration

The fluorescence of thin films of a diimine-substituted phenyleneethynylene compound can be efficiently quenched by nitroaromatic vapors, which is not the case for the unsubstituted parent compound. Thin-film porosity is usually considered to be an essential factor for efficient quenching, but in the present case the origin of the quenching is completely different, as both films are nonporous and hermetic to 2,4-dinitrotoluene (DNT) molecules. The molecular organization in the two crystallized thin films offers a low level of π stacking for both compounds, but the orientation of the phenylenethynylene fluorophore differs markedly with respect to the surface of the films. For the substituted compound, the fluorophore is almost parallel to the surface, thus making it readily available to molecules of a nitroaromatic quencher. This rationale is also observed in the case of a related compound bearing methoxy side chains instead of the long octyloxy moieties. Fluorescence-lifetime experiments show that the efficient quenching process in the nonporous crystallized films of the substituted compound is due to a fast (<70 ps) diffusion of excitons from the bulk of the film toward the surface where they are quenched, thus providing evidence of antenna effects.

Optical sensor for the detection of explosives: example of a fluorescent material

This paper deals with the detection of nitroaromatic explosives. A specific fluorescent material is devoted to the detection of ultra traces of explosives remaining on clothes. The sensor exhibits a large sensitivity for TNT or DNT vapors.

Research for the Detection of Explosives at CEA: Towards Operational Use

CEA, a prominent player in research, development and innovation has developed extensive expertise in a number of topics which are now central within the global security research issues. As an example, CEA is developing research of new technologies for the detection of explosives. This article gives an overview of the main activities regarding to the detection and identification of bulk or traces explosives. The document focus on high TRL projects aiming to develop demonstrators for testing in real configurations.