Karine Bonnot

Tunable Generation and Adsorption of Energetic Compounds in the Vapor Phase at Trace Levels: A Tool for Testing and Developing Sensitive and Selective Substrates for Explosive Detection

Among various methods for landmine detection, as well as soil and water pollution monitoring, the detection of explosive compounds in air is becoming an important and inevitable challenge for homeland security applications, due to the threatening increase in terrorist explosive bombs used against civil populations. However, in the last case, there is a crucial need for the detection of vapor phase traces or subtraces (in the ppt range or even lower). A novel and innovative generator for explosive trace vapors was designed and developed. It allowed the generation of theoretical concentrations as low as 0.24 ppq for hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in air according to Clapeyron equations. The accurate generation of explosive concentrations at subppt levels was verified for RDX and 2,4,6-trinitrotoluene (TNT) using a gas chromatograph coupled to an electron capture detector (GC-ECD). First, sensing material experiments were conducted on a nanostructured tungsten oxide. The sensing efficiency of this material determined as its adsorption capacity toward 54 ppb RDX was calculated to be five times higher than the sensing efficiency of a 54 ppb TNT vapor. The material sensing efficiency showed no dependence on the mass of material used. The results showed that the device allowed the calibration and discrimination between materials for highly sensitive and accurate sensing detection in air of low vapor pressure explosives such as TNT or RDX at subppb levels. The designed device and method showed promising features for nanosensing applications in the field of ultratrace explosive detection. The current perspectives are to decrease the testing scale and the detection levels to ppt or subppt concentration of explosives in air.

Biophotonic ring resonator for ultrasensitive detection of DMMP as a simulant for organophosphorus agents.

Combining photonic integrated circuits with a biologically based sensing approach has the ability to provide a new generation of portable and low-cost sensor devices with a high specificity and sensitivity for a number of applications in environmental monitoring, defense, and homeland security. We report herein on the specific biosensing under continuous air flow of DMMP, which is commonly used as a simulant and a precursor for the synthesis of Sarin. The proposed technology is based on the selective recognition of the targeted DMMP molecule by specifically modified proteins immobilized on photonic structures. The response of the biophotonic structures shows a high stability and accuracy over 3 months, allowing for the detection in diluted air of DMMP at concentration as low as 35 μg/m(3) (6.8 ppb) in less than 15 min. The performance of the developed technology satisfies most current homeland and military security requirements.

Chip Calorimetry for the Sensitive Identification of Hexogen and Pentrite from Their Decomposition inside Copper Oxide Nanoparticles

Smart detection systems for explosive sensors are designed both to detect explosives in the air at trace level and identify the threat for a specific response. Following this need we have succeeded in using microthermal analysis to sensitively identify and discriminate between RDX and PETN explosive vapors at trace level. Once the explosive vapor is trapped in a porous material, heating the material at a fast rate of 3000 K/s up to 350 °C will result in a thermal pattern specifically corresponding to the explosive and its interaction with the porous material. The explosive signatures obtained make it possible to simultaneously identify the presence and the nature of the explosive vapor in just a few milliseconds. Therefore, this also allows the development of multitarget devices using porous material for capturing the vapor combined with microthermal analysis for fast detection and identification. So far it is the first time that chip calorimetry has been used to characterize and identify explosives in vapor state.

Cu(OH)2 and CuO Nanorod Synthesis on Piezoresistive Cantilevers for the Selective Detection of Nitrogen Dioxide

Self-controlled active oscillating microcantilevers with a piezoresistive readout are very promising sensitive sensors, despite their small surface. In order to increase this surface and consequently their sensitivity, we nanostructured them with copper hydroxide (Cu(OH)2) or with copper oxide (CuO) nanorods. The Cu(OH)2 rods were grown, on a homogeneous copper layer previously evaporated on the top of the cantilever. The CuO nanorods were further obtained by the annealing of the copper hydroxide nanostructures. Then, these copper based nanorods were used to detect several molecules vapors. The results showed no chemical affinity (no formation of a chemical bond) between the CuO cantilevers and the tested molecules. The cantilever with Cu(OH)2 nanorods is selective to nitrogen dioxide (NO2) in presence of humidity. Indeed, among all the tested analytes, copper hydroxide has only an affinity with NO2. Despite the absence of affinity, the cantilevers could even so condensate explosives (1,3,5-trinitro-1,3,5-triazinane (RDX) and pentaerythritol tetranitrate (PETN) on their surface when the cantilever temperature was lower than the explosives source, allowing their detection. We proved that in condensation conditions, the cantilever surface material has no importance and that the nanostructuration is useless because a raw silicon cantilever detects as well as the nanostructured ones.

Self-oriented monolayer immobilization of ovalbumin and B. cereus antibody molecules on a chemically modified surface of silicon nitride fosters the enhancement of capture of bio-agents

A fast and reliable detection of biological agents in air is of a crucial importance to respond to terrorist attacks. With the aim to efficiently react to such hazards there is the need to develop highly sensitive and specific detection analytical devices for selective and quantitative detection of biological threats such as the presence of Bacillus anthracis spores and/or the presence of Ricin A toxins. In this study we explored how to achieve an oriented immobilization of antibody molecules on silicon nitride surfaces to improve their efficiency to bind to specific target molecules. In particular, we used two different methods to covalently immobilize antibody molecules on silicon nitride surfaces, and here we report the obtained results.

Investigation of the co-identification of hexogen and pentrite as particles and co-adsorbed on copper oxide nanoparticles by using nanocalorimetry

Fast-heating calorimetry experiments have been performed on a hexogen and pentrite particle mixture and on the same explosives adsorbed on CuO nanoparticles. Low heating rates allow the identification of both explosive particles. However, once adsorbed, their identification depends on their concentration ratio. An excess of PETN prevents the RDX identification.

A Biophotonic Sensor for the Specific Detection of DMMP Vapors at the ppb Level

In defense and security, there is a need to develop more sensitive and selective sensors to allow the detection of toxic and illicit compounds at trace levels. Photonic Integrated Circuits combined with specific protein bio-recognition allowed us to detect DMMP vapors down to 20 ppb in the gas phase. This strong increase in sensitivity results from the specific binding of DMMP molecules in the protein cavity. A high coverage ratio of the ring resonator with proteins permits the enhancement of the wave propagation signal resulting from the adsorption of one DMMP molecule on each biosensing protein, resulting in an amplified optical signal.