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Two UM chemistry professors are trying to solve fundamental questions about how light travels through a thin glass tube known as a capillary waveguide. The research, funded by the U.S. Department of Defense, is part of a project called the Portable Chemical Agent Detection System, which eventually could result in a hand-held chemical detector.
Such a device could dramatically improve national security, helping border patrol agents, port workers and other national security professionals detect explosives and even chemical and biological weapons.
“A big part of our effort in the past year and a half has been to characterize the waveguide itself and see how it behaves,” says Michael DeGrandpre, a chemistry professor at UM since 1996.
A solid fiber-optic cable allows light to travel uniformly down its length, but the capillary waveguide is a tube, less than half a millimeter wide, which allows chemical coatings to be applied to its inner wall. The light traveling within the tube walls interacts differently with different coatings.
Highly selective coatings are being developed to permit reliable detection of small quantities of specific chemical compounds in complex mixtures. Many of these coatings rely on the recognition capabilities of biological compounds. Associate Professor Chris Palmer, coinvestigator with DeGrandpre on the project, is working to take advantage of this chemical recognition combined with unique signatures — or “optical responses” — of different chemicals as measured by the light passing through the capillary waveguide. Eventually they want to find a chemical or biological compound to use as a coating that will react with tiny amounts of explosives or chemical warfare agents “sniffed” by the tube.
The current research uses an instrument capable of sending a wide variety of light wavelengths through the capillary waveguide and another capable of reading the broad spectrum of light. The researchers measure how different chemical coatings in the inner tube respond with the light sent through. Right now, the equipment is hardly portable, occupying space the size of an average kitchen table.
bench-top instrument, they hope to settle on specific chemistries for
the inner capillary that will generate a specific optical response
when exposed to a whiff of explosive or dangerous weapons hovering
in the air at concentrations as low as one part per billion. When they
achieve that, they can work on shrinking the device to the size of
a small flashlight. Palmer says it might take two years before they
have a bench-top instrument capable of detecting explosives or chemical
The Portable Chemical Agent Detection System is part of a growing number of projects funded by the Department of Defense aimed at using technology to bolster the nation’s defenses against would-be terrorists. DeGrandpre says there is a large effort to improve chemical- sensing technology for a wide variety of applications. At a recent American Chemical Society meeting, a majority of papers dealt with various terror-related chemical sensor projects.
Until this new technology becomes available, national security experts can still fall back on a relatively simple, but highly effective, chemical and biological detection system — specially trained dogs.