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ATLANTA -- Should terrorists use chemical or biological
weapons against the United States, new sensing technologies being
developed at the Georgia Institute of Technology could help public
safety officials respond more rapidly and effectively to the threats.
For example, chemical sensors in building ventilation systems
could detect a release of gas intended to harm the occupants. The
detection might then trigger a shutdown of the ventilation system,
says optical sensor developer Dan Campbell, a senior research
scientist at the Georgia Tech Research Institute (GTRI). He recently
presented an American Chemical Society invited lecture on using
sensor technologies to counter terrorism.
Chemical sensors could also be mounted on an unmanned aerial
vehicle (UAV) to track a chemical plume, giving emergency managers
insight on evacuation plans, Campbell suggests. And rapid biological
sensors could be incorporated into handheld devices for first
responders investigating a suspicious package.
"Many sensor technologies under development are becoming reliable,
versatile, inexpensive and presumptive -- they can help first
responders make a reasonable assessment," Campbell notes.
At Georgia Tech, work has been under way on sensing technologies
that could not only improve homeland security, but also enhance
response to industrial accidents, environmental pollution and
Here, we feature three of the numerous Georgia Tech projects aimed
at creating better methods and practical applications of these
Multi-Purpose Optical Sensor
Campbell and his GTRI colleagues have been developing an
integrated-optics sensor that can detect the presence of biological
agents in minutes and chemical agents in seconds. They are tuning the
sensor for detection of industrial pollutants, food-borne pathogens
and, most recently, agents associated with terrorist attacks. The
U.S. Marine Corps Warfighting Laboratory and Marine Corps Systems
Command supported the latter research.
The sensor, which may cost significantly less than current
devices, consists of a laser light source, a planar waveguide
(essentially a small piece of glass through which the light travels)
and a detector for monitoring light output.
Reactions on the waveguide surface alter the speed of light
through the waveguide. This change is monitored with an
interferometer by comparing a reference beam with another beam
traveling under the sensing chemistry. Signal processing software
interprets the sensor's results and delivers information on the
agents' identity and quantity. The waveguide chip is small enough
that it can accommodate several sensing channels designed to detect a
wide variety of chemical and biological agents.
"We've built one platform for all possible uses, both in the air
and in the water," Campbell explains. "You don't change out the laser
or detector. You just plug in the chip you need and you're ready to
Researchers have successfully and rapidly detected numerous agents
-- including Salmonella and Campylobacter bacteria, anthrax, ricin,
chlorine and ammonia -- in laboratory tests, as well as groundwater
contaminants such as chlorinated hydrocarbons in field tests.
Recently, they have improved the sensor's reliability and sought
new applications for the technology. To sense biological agents, the
device takes rapid, direct measurements of the binding of an antigen
to a chemical receptor on the waveguide surface.
Researchers previously used antibodies as receptors. But they are
more expensive and less reliable than aptamers, the synthetic,
nucleic-acid-based receptors used in the sensor now, Campbell says.
GTRI research scientist Jie Xu has been assisting Campbell with the
Aptamers have been available for more than a decade, but haven't
been used much until recently. "The aptamers are rock stable,"
Campbell says. "They work the same way every time. And they are
reusable and basically cheaper to make than antibodies."
GTRI is exploring several opportunities for its sensor. The U.S.
Naval Research Laboratory and the Marine Corps Warfighting Laboratory
are seeking applications for their Dragon Eye mini-UAV (unmanned
aerial vehicle). The reconnaissance device, which can be launched by
hand or with a bungee cord, can fly one-hour missions within a 6-mile
radius of the launch site. So GTRI researchers are testing the
operation of the chemical sensor mounted in the UAV's nose cone.
Campbell successfully demonstrated the idea at a recent defense
technologies conference. But he wants to shrink the sensor from its
current one-half-pound size to about one ounce. Then he plans to
mount a sensor on each of the Dragon Eye's wings to get a more
precise reading on the source of a chemical plume, he explains. The
same concept could then apply to a remotely operated roving vehicle
or one that could swim, Campbell adds.
Meanwhile, Campbell has just begun work for AIMSI, an Oak Ridge,
Tenn., company that wants to use GTRI's sensing technology in a
handheld device for first responders and a groundwater monitoring
device for environmental professionals. Also, Campbell's GTRI
colleague David Gottfried is collaborating with the University of
Georgia's Center for Food Safety to develop the sensing chemistry to
detect infectious disease agents, including potential bioweapons, in
water, fruit juice, milk, food and the environment.
Fully Integrated Sensing Systems
Researchers from several universities, including Georgia Tech, are
collaborating on the development of integrated micro-optical sensors
for chemical and biological agents of national security concern. The
goal is to merge optical sensing technology -- like GTRI's -- with
highly integrated electrical circuits into a fully integrated sensing
system on a silicon chip.
"The advantages of this system will be better performance, a
smaller size that uses less power, full integration and a low cost of
only a few dollars per chip," explains Stephen Ralph, the Georgia
Tech School of Electrical and Computer Engineering associate
professor who is leading a $1.5 million part of the research effort.
"This is our vision. We still have a lot of science and engineering
to do to merge these technologies into a fully integrated system."
The optical sensing technology is this: A source emits light that
passes into a piece of silicon nitride, which serves as a waveguide.
This silicon nitride is also an interferometer, which divides the
light into two separate paths. On one path, a polymer absorbs the
agent being investigated, and on the other path, a reference, no
agent is absorbed.
After passing through these two paths, light is recombined by the
interferometer. This separation and recombination of light detects
relative changes in the optical refractive index caused by the
absorbed agent. The recombined signal is optimized with signal
processing software to enhance sensitivity. The result is an
interference pattern that changes when an agent contacts the sensor.
Now in its fourth year, this proof-of-concept stage has been
funded by the Defense Advanced Research Projects Agency (DARPA)
through the University of Illinois.
"The remarkable advantage of a fully integrated system is the
ability to apply dynamic signal enhancement strategies to improve
sensitivity and selectivity while reducing the likelihood of false
positives," Ralph says. "We have fabricated a fully integrated
system, although challenges remain in the integration of the optical
sources in an efficient manner with the rest of the chip."
Researchers have not yet tested the sensor with any agents of
concern, but have experimented with compounds having similar
properties and demonstrated sensitivities in the hundreds of
parts-per-billion range using their signal enhancement strategies.
Additional funding will enable tests of "mock" agents that have
similar chemical composition to the substances terrorists might use.
Then, they hope to make the device more sensitive and address
fabrication issues that will affect manufacturing yield and cost,
The Georgia Tech-based research team involves Ralph and Associate
Professor of Chemical Engineering Cliff Henderson and their graduate
students. Working with them are former Georgia Tech Professor Nan
Jokerst and Associate Professor Martin Brooke, now at Duke
Meanwhile, their collaborators at Colorado State University and
the University of Michigan are working on microfluidic sensors with a
fully integrated design. These devices will detect agents in liquid
form as they flow through micro channels created by integrated
circuits technology..When light passes through or near these
channels, a change in a fluid's optical properties would indicate the
presence of a particular agent of concern.
Also, researchers at the University of Illinois, which is
administering the overall project for DARPA, are working on optical
sensors that detect agents in the far infrared part of the spectrum.
"Some of these technologies under development will prove to be
more effective with certain agents than others, while some will be
more integrated than others," Ralph says in explaining the
multi-university, multiple technologies approach. "There will be a
tradeoff between selectivity, sensitivity and cost. So there's not
just one solution, but many depending on the application."
Detecting Changes in Fluorescence in Polymers
A type of highly fluorescent polymers called PPEs, or
poly(paraphenyleneethynylene), could be the basis for a chemical
sensing system that would detect pathogens and toxins that might be
used in a bioterrorism attack. The agents of concern include cholera,
anthrax and ricin.
"Fluorescence is very sensitive to the chemical environment," says
Uwe Bunz, a Georgia Tech professor of chemistry and biochemistry. "So
it's a very good tool to report changes."
With a one-year, proof-of-concept grant from the National
Institutes of Health, Bunz is exploring the feasibility of detecting
changes in the fluorescence or color of PPEs when they interact with
a pathogen or toxin. But the goal has presented some technical
PPEs are typically not soluble in water, but for use as sensors,
they must be, Bunz says. So researchers added very polar, water-like
extensions to the lipophilic, or butter-like, substituent chemical
side chains that extend from the long chemical backbones that form
PPEs. "This achievement was very important because we live in a
water-based world," Bunz notes. "Everything with biological
importance has to be looked for in water."
Researchers must also make PPEs mimic the sensing functions of
human cells in a primitive way, Bunz explains. On the surface of
pathogens and some toxins are proteins called lectins that bind with
sugar molecules on the surface of human cells to attack them.
Similarly, Bunz wants to add sugar molecules to the chemical side
chains that extend from PPEs. Then he will see if these sugars bind
Researchers have been synthesizing a library of PPEs and other
polymers with sugars attached, and they have begun early-stage
testing of these materials.
"We don't want to work with something like anthrax right now, so
we're testing these polymers with free lectins to see if we can
detect lectin binding with the polymer," Bunz explains. "We're
looking for a change in the amount of fluorescence or a change in the
color of fluorescence.
"We've done a little of this lectin sensing, but to do this
better, we need to use longer extendable linkers for the sugars
attached to our polymers," Bunz says. "It's a major challenge to do
But Bunz is hopeful that his research team can overcome the
technical obstacles they face and eventually find military, homeland
security and medical applications for this technology, he says.
One scenario he envisions would be a field test kit that first
responders could use if they found a suspicious package. Hazardous
materials personnel could dissolve some of the package's content in
water, add Bunz' polymer solution and then use a black light to
quickly determine a change in the polymer's fluorescence or color. If
the concept proves feasible, Bunz will seek additional funding and
collaborate with a biosafety laboratory that can work with the
pathogen anthrax and/or the toxin ricin.
"If we can make the links longer and then detect a change in
fluorescence with the addition of 1,000 or even 10,000 lectin
molecules, then we'll know we have something really good," Bunz adds.
For more information, please contact Dan Campbell Dan Campbell,
Senior Research Scientist, Georgia Tech Research Institute, Atlanta,
GA 30332-0841, 404-894-3627, fax 404-894-7452,
email@example.com; or Associate Professor Stephen
Ralph, School of Electrical and Computer Engineering, Georgia Tech,
Atlanta, GA 30332-0250, 404-894-5168, fax 404-894-4641,
firstname.lastname@example.org; or Professor Uwe Bunz, School of
Chemistry and Biochemistry, Georgia Tech, Atlanta, GA 30332-0400,
404-385-1795, fax 404-894-7452, email@example.com.
From Research Horizons, published by the Georgia Tech Research
News & Publications Office.
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