WASHINGTON - A group of scientists have discovered a new way to sensitively detect explosives based on the physical properties of their vapors.
“Certain classes of explosives have unique thermal characteristics that help to identify explosive vapors in presence of other vapors,” said Thomas Thundat, a researcher at Oak Ridge National Laboratory (ORNL) and the University of Tennessee, who conducted the research with his colleagues at ORNL and the Technical University of Denmark.
In their research, the scientists show that their technology is capable of trace detection of explosives.
They also show that it is capable of distinguishing between explosive and non-explosive chemicals and of differentiating between individual explosives, such as TNT, PETN, and RDX.
Typical sensors use ion mobility spectrometers, which ionize tiny amounts of chemicals and measure how fast they move through an electric field.
While these instruments are fast, sensitive, and reliable, they are also expensive and bulky, leading many researchers in the last few years to try to find a cheaper, more portable device for detecting explosives.
The new research focused on “micromechanical” devices, which are tiny sensors that have microscopic probes on which airborne chemical vapors deposit.
When the right chemicals find the surface of the sensors, they induce tiny mechanical motions, and those motions create electronic signals that can be measured.
These devices are relatively inexpensive to make and can sensitively detect explosives, but they often have the drawback that they cannot discriminate between similar chemicals - the dangerous and the benign.
Seeking to make a better micromechanical sensor, Thundat and his colleagues realized they could detect explosives selectively and with extremely high sensitivity by building sensors that probed the thermal signatures of chemical vapors.
They started with standard micromechanical sensors - devices with microscopic cantilevers beams supported at one end.
They modified the cantilevers so that they could be electronically heated by passing a current through them.
Next, they allowed air to flow over the sensors. If explosive vapors were present in the air, they could be detected when molecules in the vapor clung to the cantilevers.
Then, by heating the cantilevers in a fraction of a second, they could discriminate between explosives and non-explosives.
All the explosives they tested responded with unique and reproducible thermal response patterns within a split second of heating.
The researchers are now improving the sensitivity and making a prototype device, which they expect to be ready for field testing later this year.
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