Gas chromotography and mass spectrometry are long-standing
standard methods of chemical analysis. If you want to know the
composition of an airborne chemical, these methods are commonly used. However,
these methods traditionally require a lab setup and are of limited practical
use in the real world. So what about practical, real world situations
like an airport detector of plastic explosive, or a industrial plant monitor to
determine if toxins have entered the air -- how could these more complex in-the-field
type uses be made reality?
One approach is to try to reinvent the wheel and develop new and exotic
sensors. Using neural networks, novel chemistry, and quirky algorithms
are among the methods tried in this approach. The far simpler, but more
difficult to implement solution is to merely take the proven methods and shrink
them to a microscopic scale.
Taking the latter approach is a daunting task, but engineers at MIT'S
Microsystems Technology Laboratories (MTL) are determined to do just that, and already achieved significant progress in
developing an portable electronic "nose".
MIT Professor Akintunde Ibitayo Akinwande envisions the final product to be a
detector the size of a matchbox. Akiwande restated the proven nature of
the technology, saying, "Everything we're doing has been done on a macro
scale. We are just scaling it down."
The key is converting macro scale into micro mechanical components and then
integrating them with electrical devices. These kinds of systems are
known as Micro Electro Mechanical Systems (MEMS), a burgeoning
field of technology. The MTL lab is a leader in the development of
these kinds of systems.
Dr. Akinwande and MIT research scientist Luis Velasquez-Garcia will present
their work at a conference next week. They will then present a further
update on the progress in December. Dr. Akinwande's team has the support
of a large international group of participants including scientists at the
University of Cambridge, the University of Texas at Dallas, Clean Earth
Technology and Raytheon.
Currently, there are backpack-sized gas chromatography and mass spectrometry
(GC-MS) sensors, but their large size makes them impractical and they are very
slow. They can take up to 15 minutes to get a result and consume lots of energy
-- 10 kJ of energy. Dr. Akinwande and his team's matchbox-sized device
consumes a scant 4 Joules and produces results in about 4 seconds.
The condensed version works by first breaking down the gas sample into
fragments and ionizing these fragments, which are identified by specific charge
(ratio of charge to molecular weight). The gas molecules are
broken apart by stripping their electrons or by the more novel approach of
bombarding them with electrons stripped from carbon nanotubes; yet another
use for the multifunctional nanotubes. The resultant ion charges are
converted to voltage after being sent through an electric field. This
voltage is measured and gives the molecule's unique electric fingerprint,
revealing its identity.
One key advantage of taking the device to a micro scale is that the vacuum
necessary in the chamber with the electric field is much more costly in terms
of energy to maintain. Batch production similar to IC production will
allow the devices to be produced more easily and effectively than traditional
macroscopic hand-assembled models.
The research started three years ago and is funded by Defense
Advanced Research Projects Agency (DARPA) and the U.S. Army Soldier Systems
Center in Natick, Mass. The team states that the device will be complete
and ready to be adapted for mass production within 2 years. It will
surely have a major impact on the fields of security, environmental science,
public safety, and defense.