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  • Chemical Sensor Offers Sensitive Real-Time Solution

Photonics Spectra
Feb 1999
Aaron J. Hand

A sensor developed at the Georgia Tech Research Institute could make detection of chemical contaminants highly portable and sensitive, and also enable in situ monitoring of a range of chemicals. It is a planar optical waveguide chip with 13 interferometric sensors built onto it. Each interferometer acts as a sensor channel, containing a chemically selective film that reacts to refractive index changes.
"The problem in the past has been developing something sensitive enough to detect the chemicals," said Nile Hartman, principal research engineer at the institute's Electro-Optics, Environment and Materials Laboratory and the sensor's inventor. His device can detect chemicals in the parts-per-billion range, he said.
The sensor uses a standard laser diode with a wavelength of 670 to 780 nm. The device's sensitivity depends on the contaminants it is trying to detect -- with reactive chemistries, for example, offering increased sensing capabilities -- but the researchers can tailor the chemistries to detect chemicals that would otherwise be more difficult to pinpoint.
"Since we're using refractive index change instead of fluorescence or absorption, it opens up a whole new class of surface chemistries we can work with," Hartman said. "We're looking at very, very small index changes." Because the reaction is reversible, it allows the sensor to be used for in situ monitoring.
The device can detect vapor- and aqueous-phase contaminants. Detection is around 100 parts per billion for BTEX compounds (benzene, toluene, ethyl benzene and xylene), which may be found in groundwater. Ammonia -- a vapor-phase contaminant -- can be detected easily because it is a reactive surface chemistry. Hartman has also used the sensor for biological testing, detecting foodborne pathogens in a carcass wash.
The sensor is the heart of a system -- the Environmental Systems Management, Analysis and Reporting Network -- that includes data management tools.
Researchers expect a field test for the system to begin early this year to detect BTEX compounds from aircraft cleaning agents that have seeped into soil and groundwater. The sensors will be placed in cone penetrometers in the ground.
Atlanta-based Photonic Sensor Systems Inc., of which Hartman is part owner, has an exclusive license to commercialize the technology. "With a real push and proper funding it could be commercially available within a year," he predicted.

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