Sniffing out the gases with E-nose

11 July 2016
Posted by Lucka Bibic.

A new chemical sensor, or "electronic nose" has been developed that can spot even the tiniest amounts of gas, providing a new tool in the fight against terrorism.

In a surprisingly large number of cases, you need to detect a very low concentration of a gas molecule in the air around you. "Examples include chemical warfare or smelling food that has gone bad," says Dr Rob Ameloot, whose highly sensitive electronic "nose" targets these dangerous gases.

Imagine equipping your smartphone with a tiny sensor that could check your food for very minute amounts of pesticides or even detect nerve gases. As this sounds - or smells like a very good idea, Ameloot and other researchers are now leading an effort to develop a highly sensitive portable chemical sensor that can absorb and rapidly detect extremely low amounts of harmful nerve gases.  

Unlike light and sound, smell is not energy, but mass - and when you smell something, you sense chemical molecules in the air. Similarly, an electronic nose detects chemical compounds using solid materials with honeycomb-like structures, made up of metal ions connected by organic molecules with the porous cavities in between.

Such materials are known as metal-organic frameworks or MOFs. Resembling a spongy ultrathin film, the holes in MOFs are nanometer-sized which make them a thousand times smaller than the diameter of a human hair. These molecular blocks are tailored for trapping the bulky phosphonates found in pesticides and chemical gases such as sarin.

The new system can breathe in low levels of chemical agents and allow them to enter into interior space of MOFs. The size and shape of the pores in this material can be altered to detect a specific gas by merely modifying the structure of either the organic or metal molecules. Their high surface areas and open sponge-like structure make them ideal for absorbing different gases.

Upon the contact of the specific chemical agent with a well-designed MOF material, the spongy surface translates its chemical message into electrical signal and reports it to an attached electrical probe.

By detecting these electrical changes on the metal-organic surface, the sensor can nose out one molecule in a billion of others and pick up on even the cleverest wrongdoer, hiding the chemical weapon.

In the wake of the rise in international terrorism, combined with improvised explosives, the current terrorism threat to the UK was raised to severe. As an attack is highly likely, this highlights the need for sensitive sensors that would rapidly detect chemical weapons.

A current limitation of these sensors is their inability to pick up ultra-traces of gas analytes in the air and the idea of a smoke-detector-like device sounding an alarm when a terrorist enters a train station might be years from fruition.

But still, the development of the electronic nose is the next step in a world free from chemical weapons.

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