Research in Explosive Detection
Much of this research focuses on “micromechanical” devices — 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. They may detect a trace amount of TNT, for instance, but they may not be able to distinguish that from a trace amount of gasoline.
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. In their paper, Thundat and his colleagues demonstrate that they could detect very small amounts of adsorbed explosives — with a limit of 600 picograms (a picogram is a trillionth of a gram). They are now improving the sensitivity and making a prototype device, which they expect to be ready for field testing later this year.
Here’s the paper, behind a paywall.