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Study of ultrafine traces of energetic materials

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- Tunable generation of explosive vapors for investigating the affinity of sensors
- Study of energetic materials by nanocalorimetry
- Detection of explosive traces with bio-inspired systems

- Denis Spitzer <>
- Karine Bonnot <>


There is a need for systems that can detect explosives, chemical warfare agents (CWA) or even drugs in ultrafine traces, in the form of vapors or particles. Their sensitivities must present a breakthrough compared to existing techniques. We are working on techniques both for the vapor and the solid phase (i.e. particles).

There are to important prerequisites for this research:

- Being able to generate vapors of explosives (and other substances) in very low, controlled and tunable concentrations. We successfully developed and validated such a system.
- Measuring the adsorption of explosives on layers of sensitive materials in a quantitative way for the validation of a sensor. We carry out such tests based on a flow cell and downstream gas measurements by GC/MS/ECD.

The particle approach: nanocalorimetry for detection

Photo of a nanocalorimeter chip
Photo of a nanocalorimeter chip

The nanocalorimeter has been originally developed as a way to do thermal analysis on very small samples. The thermal behavior is a unique signature that can be used for the identification of a substance.

This leads to the use of nanocalorimetry as a tool for detection that enables the identification of a single explosive particle, for example for the surface of clothing or of a baggage item. The analysis takes only a few milliseconds and is extremely sensitive: it allows to detect as little as 600 femtograms of RDX or PETN, and even 40 femtograms of CL-20.

Thermal analysis by nanocalorimetry
Thermal analysis by nanocalorimetry
Nanocalorimetry traces of the explosives PETN (left) and RDX (right), obtained from a single micron-sized particle in less than one second.

The vapor-phase approach: bio-inspired sensor systems

Most explosives have a very low vapor pressure at room temperature — on the order of a few ppb (parts per billion). Sensors for explosive vapors must thus be very sensitive and selective.

Bio-inspired explosive detection system
Bio-inspired explosive detection system
The sensilla of the butterfly bombyx mori (A—C) inspired the creation of this sensor, an AFM microcantilever covered with TiO2 nanotubes. © 2012 Wiley-VCH.

We recently presented a bio-inspired detector based on an AFM cantilever covered with TiO2 nanotubes. This system has been inspired by the sensilla of the silkmoth bombyx mori. Its selectivity is due to the strong affinity of titanium dioxide for nitro explosives.