Mechanical nose to match dogs

Scientists have invented a mechanical nose to sniff out explosive vapours from a terrorist at an airport.

The aim is to screen passengers and their luggage for explosives as they pass through a scanner similar to those used to detect metal. The way explosives are detected now is by swabbing a person's briefcase or laptop - a time-consuming practice.

Bonner Denton, professor of chemistry at the University of Arizona in Tucson, says putting the device in a walk-through scanner would make it feasible to screen every passenger rather than only those who have aroused suspicion.

"This is more sensitive than a dog's nose. It does not suffer from over exposure, and it tells you what material has been detected. Dogs just tell you something's been detected," Professor Denton says.

Detecting explosives or drugs means sorting through a plethora of scents, vapours and other chemical signals to pick out one substance of interest. A dog's nose is exquisitely sensitive to thousands of smells and can pick out one scent against background "noise" if trained to do so.

To do the same thing mechanically requires using a technology called ion mobility spectrometry. Ions, or charged molecules, move when placed in an electric field. The speed at which an ion moves depends on its size and shape, so each ion moves at a characteristic speed.

Airport analysers collect chemicals gathered from a person's luggage, put those chemicals into an electric field and then search for any ion that has a speed that indicates "explosive".

The machine needs a certain number of molecules to accurately detect and identify a specific chemical. If there are very few molecules of a particular substance, the machine cannot distinguish that molecule from all the others in the mix. Denton realised that one place to improve detection was the electronics of ion mobility spectrometers. So he adapted circuitry originally developed for infra-red astronomy.

The new device, called a capacitive transimpedance amplifier, improves the readout circuitry. "This change in readout electronics boosts the signal while lowering the noise," Denton says. "This is the first radical change in ion detection since the 1930s."

- INDEPENDENT