[Editors] MIT uses nanotubes to sense deadly gases

[Elizabeth Thomson]

For Immediate Release
WEDNESDAY, JUNE 11, 2008
Contact: Elizabeth A. Thomson, MIT News Office -- Phone: 617-258-5402  
-- Email: thomson at mit.edu

PHOTO, IMAGES AVAILABLE
Story online at http://web.mit.edu/newsoffice/2008/nanotube-0605.html

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MIT uses nanotubes to sense deadly gases

--Most sensitive detector yet for sarin, more
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CAMBRIDGE, Mass.--Using carbon nanotubes, MIT chemical engineers have  
built the most sensitive electronic detector yet for sensing deadly  
gases such as the nerve agent sarin.

The technology, which could also detect mustard gas, ammonia and VX  
nerve agents, has 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.

“We think this could be applied to a variety of environmental and  
security applications,” said Michael Strano, the Charles and Hilda  
Roddey Associate Professor of Chemical Engineering and senior author  
of a paper describing the work published recently in the online  
edition of Angewandte Chemie.

Strano's sensor has exhibited record sensitivity to molecules  
mimicking organophosphate nerve toxins such as sarin: It can detect  
minute quantities as low as 1 femtomole (1 billion molecules),  
roughly equivalent to a concentration of 25 parts per trillion.  
“There's nothing that even comes close,” he said.

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.

To build their super-sensitive detector, 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 about 1/50,000 of the width of a human  
hair, which acts as a molecular wire.

The nanotube sensors require very little power-about 0.0003 watts.  
One sensor could run essentially forever on a regular battery. “It's  
something that could sit in the corner of a room and you could just  
forget about it,” Strano said.

When a particular gas molecule binds to the carbon nanotube, the  
tube's electrical conductivity changes. 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.

The new MIT sensor is also the first nanotube sensor that is  
passively reversible at this level of sensitivity. To achieve this,  
the team needed to decrease how strongly the nanotube sensor binds  
different gas molecules on its surface, allowing the sensor to detect  
a series of gas exposures in rapid succession.

Using a newly described chemistry outlined in a separate paper  
published in January in the Journal of the American Chemical Society,  
Strano and co-workers showed that this can be done by coating the  
nanotubes with amine-type molecules, which donate an extra pair of  
electrons to the nanotubes.

The coating allows gas molecules to bind to nanotubes but detach a  
few milliseconds later, allowing another molecule from the column to  
move in. With a network of these reversible sensors, a gas could be  
tracked as it spreads through a large area.

The lead author of the paper is Chang Young Lee, a graduate student  
in chemical engineering. Richa Sharma, another MIT graduate student  
in chemical engineering, is also an author of the paper. Adarsh  
Radadia and Richard Masel at the University of Illinois at Urbana- 
Champaign developed the microcolumn technology.

The work was funded by the Department of Homeland Security under  
contract to the Federal Aviation Administration and MIT's Institute  
of Soldier Nanotechnology. Characterization facilities used for this  
work were supported by the Department of Energy. Microcolumn and  
detector development was funded in part by the Defense Advanced  
Research Projects Agency.

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Written by Anne Trafton, MIT News Office