Energy-efficient device could quickly detect hazardous chemicals (fwd)

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MIT gas sensor is tiny, quick

Energy-efficient device could quickly detect hazardous chemicals

Anne Trafton, News Office

January 10, 2008

http://web.mit.edu/newsoffice/2008/micro-analyzer-0110.html

Engineers at MIT are developing a tiny sensor that could be used to detect

minute quantities of hazardous gases, including toxic industrial chemicals and

chemical warfare agents, much more quickly than current devices.

The researchers have taken the common techniques of gas chromatography and mass

spectrometry and shrunk them to fit in a device the size of a computer mouse.

Eventually, the team, led by MIT Professor Akintunde Ibitayo Akinwande, plans to

build a detector about the size of a matchbox.

" Everything we're doing has been done on a macro scale. We are just scaling it

down, " said Akinwande, a professor of electrical engineering and computer

science and member of MIT's Microsystems Technology Laboratories (MTL).

Akinwande and MIT research scientist Velasquez- plan to present their

work at the Micro Electro Mechanical Systems (MEMS) 2008 conference next week.

In December, they presented at the International Electronic Devices Meeting.

Scaling down gas detectors makes them much easier to use in a real-world

environment, where they could be dispersed in a building or outdoor area. Making

the devices small also reduces the amount of power they consume and enhances

their sensitivity to trace amounts of gases, Akinwande said.

He is leading an international team that includes scientists from the University

of Cambridge, the University of Texas at Dallas, Clean Earth Technology and

Raytheon, as well as MIT.

Their detector uses gas chromatography and mass spectrometry (GC-MS) to identify

gas molecules by their telltale electronic signatures. Current versions of

portable GC-MS machines, which take about 15 minutes to produce results, are

around 40,000 cubic centimeters, about the size of a full paper grocery bag, and

use 10,000 joules of energy.

The new, smaller version consumes about four joules and produces results in

about four seconds.

The device, which the researchers plan to have completed within two years, could

be used to help protect water supplies or for medical diagnostics, as well as to

detect hazardous gases in the air.

The analyzer works by breaking gas molecules into ionized fragments, which can

be detected by their specific charge (ratio of charge to molecular weight).

Gas molecules are broken apart either by stripping electrons off the molecules,

or by bombarding them with electrons stripped from carbon nanotubes. The

fragments are then sent through a long, narrow electric field. At the end of the

field, the ions' charges are converted to voltage and measured by an

electrometer, yielding the molecules' distinctive electronic signature.

Shrinking the device greatly reduces the energy needed to power it, in part

because much of the energy is dedicated to creating a vacuum in the chamber

where the electric field is located.

Another advantage of the small size is that smaller systems can be precisely

built using microfabrication. Also, batch-fabrication will allow the detectors

to be produced inexpensively.

The research, which started three years ago, is funded by the Defense Advanced

Research Projects Agency and the U.S. Army Soldier Systems Center in Natick,

Mass.

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