Using carbon nanotubes, MIT chemical engineers have built the most sensitive electronic detector yet for sensing deadly gases such as the nerve agent sarin, coupling the nanotubes with a miniature gas-chromatography column and separating different gases.
The technology, which could also detect mustard gas, ammonia and deadly VX nerve agents, has the potential to be used as a low-cost, low-energy device that could be carried in a pocket or deployed inside a building to monitor hazardous chemicals.
To build the super-sensitive detector, Professor Michael Strano and his team used an array of carbon nanotubes aligned across microelectrodes. Each tube consists of a single-layer lattice of carbon atoms, rolled into a long cylinder with a diameter of around 1/50,000 of the width of a human hair, which acts as a molecular wire.
Nanotube sensors require very little power, about 0.0003 watts and one sensor could run essentially forever on a regular battery. When a particular gas molecule binds to the carbon nanotube, the tube’s electrical conductivity changes and as each gas affects conductivity differently, so gases can be identified by measuring the conductivity change after binding.
The researchers achieved new levels of sensitivity by coupling the nanotubes with a miniature gas-chromatography column etched onto a silicon chip smaller than a penny. The column rapidly separates different gases before feeding them into the nanotubes.
“We think this could be applied to a variety of environmental and security applications,” said Strano, the Charles and Hilda Roddey Associate Professor of Chemical Engineering and senior author of a paper describing the work published this week in the online edition of Angewandte Chemie.
Strano’s sensor has exhibited record sensitivity to molecules mimicking organophosphate nerve toxins such as sarin.
Sarin, which killed 12 people in a 1995 terrorist attack on the Tokyo subway, can kill at very low concentrations (parts per million) after 10 minutes, so highly sensitive detection is imperative to save lives. The new detector is far more sensitive than needed to detect lethal doses.
The new MIT sensor is also the first nanotube sensor that is passively reversible at this level of sensitivity, achieving this by decreasing how strongly the nanotube sensor binds different gas molecules on its surface and allowing the sensor to detect a series of gas exposures in rapid succession.