Scientia: Research at the University of Tennessee
Frontline Microbes
By KRIS CHRISTEN
Innovative devices—part machine, part living organism—may soon probe the battlefield for hidden dangers or detect contaminants lurking in food and water
Imagine a fingernail-sized sensor that could provide an early warning if a chemical or biological contaminant has infiltrated your food or water supply. Or picture a device capable of detecting explosives buried in soils and alerting soldiers to possible dangers lurking on the battlefield. Researchers at the University of Tennessee have teamed up to create just such a sentinel to monitor a multitude of harmful chemicals and bacteria on in real time. The work, still in the development phase, builds on the biosensor technology patented by UT's Center for Environmental Biotechnology (CEB).
The biosensors are made up of tiny computer chips layered with living bioluminescent microorganisms that are genetically engineered to emit light when they are exposed to the targeted substance. Microluminometers attached to the sensor chip detect and process the light signal, then send the name and approximate concentration of the contaminant to a remote data-collecting unit.
These detectors were initially developed for monitoring a wide range of environmental contaminants. Now the researchers hope to take the technology a step further, into the realm of military intelligence and homeland security. "We're trying to develop a new capability for the military to understand the environmental exposures experienced by troops in the field—chemical and biological exposures in food, water, and the general military environment," explains Gary Sayler, CEB's director. (Sayler also serves as director of the UT–Oak Ridge National Laboratory Joint Institute for Biological Sciences.) Ultimately, he says, the military wants to better "understand what their battle-fighters are being exposed to and predict how that could affect the quality of what they're able to do."
Harnessing Nano-Power
These so-called "bioluminescent bioreporter integrated circuits" are currently capable of detecting one contaminant per chip. Under a grant from the U.S. Department of Defense's Office of Naval Research, however, CEB and researchers from ORNL are now employing nanofibers to allow them to detect a wider range of contaminants with one sensor. "We have the chip, we have the bioreporters, we have the nanofibers; it's just a matter of merging these three proven technologies into one and to get it to work," says Steven Ripp, a research assistant professor at CEB.
Plans call for incorporating carbon nanofibers directly onto the chips in a precise pattern and then tethering the biological systems to the nanofibers. "We can arrange these nanofibers so that they provide a little cage, like a micro-zoo, to contain the organisms that will do the detection," explains Anatoli Melechko, a research assistant professor in UT's Materials Science and Engineering Department and a physicist at ORNL's Center for Nanophase Materials Science.
The nanofibers offer a larger surface area, allowing more sensing elements to be placed on one chip, Sayler says. And since these organisms can be held in place in these virtual cages, "we'll have an opportunity to provide better conditions for feeding and maintaining them," Sayler says, adding that "we expect that the sensor will be more sensitive, as well," which could make it possible to detect pathogenic microbes in very dilute samples of water or food.
Plants as Allies
On another front, researchers at UT's Agriculture Experiment Station have a grant from the U.S. Armed Forces Medical Intelligence Command to adapt CEB's biosensor and bioluminescence technology for use in plants and algae. Theoretically, such phytosensors could be sown from an airplane to passively monitor wide swaths of territory for potentially dangerous chemicals, says Neal Stewart, a plant molecular geneticist with UT's Department of Plant Sciences.
The power of using plants or algae as sensors lies in their ubiquity throughout the environment, their ability to concentrate and sequester contaminants in tissues, and their responsiveness, according to Stewart. Whereas motile animals can walk, swim, wriggle, or jump away when they detect contaminants in the environment, plants and algae respond biochemically to such threats by turning on genes for various protective responses. "We're trying to use what nature has given us here," he explains. In other words, if we can engineer sensors in these plants and algae to emit a signal when they come encounter a particular contaminant, and that signal could be monitored remotely, possibly even by satellite, "we might be able to tell what's there—maybe even at what concentration—without ever having to hit the ground," Stewart says. For example, plants could prove useful in detecting the chemicals leaching from a land mine. Similarly, algae placed downstream of a suspicious facility might be able to alert military intelligence analysts to what's being produced there.
The researchers have a number of challenges to overcome in building such sensors, not least of which is developing a system that can work in all kinds of conditions, including high heat and low humidity. "Those are very difficult conditions for the biological sensor to deal with, and we have to optimize for that," Sayler notes. Stewart also has his work cut out for him in getting the bioluminescence genes to work in higher organisms and produce enough light to be detected remotely.
Widespread Application
If they're successful, these technologies could result in low-cost real-time techniques for covert wide-area surveillance monitoring, with a unique capacity for detecting large numbers of contaminants at minute concentrations, according to Sayler. "If we can do these things, it'll be inexpensive, you won't require large equipment, and you could have lots of simple sensory elements out in the environment," he says.
Apart from military intelligence applications, these technologies have a range of other possibilities, as well, from detecting bacterial pathogens in food and pinpointing pollution sources and their effect on people or crops to monitoring water quality in streams or air quality in such enclosed environments as shopping malls or even spacecraft. The National Aeronautics and Space Administration has expressed interest in that last application.
Similarly, phytosensors planted in fields conceivably could be designed to produce a light or change color if they encounter an agroterrorism agent or a particular plant disease—soybean rust, for example. This serious agricultural pest, which has caused widespread crop losses in Southern Africa and South America, entered the United States in 2004. Biosensor technology, combined with precision agriculture global positioning systems, "could help us monitor where that's going on and how it's affecting farmers' crops," Stewart says.
"Eventually, we're hoping too to move this technology into medical diagnostics and therapeutic screening for particular diseases, like cancer," Sayler adds.
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For more information, contact Steven Ripp, (865) 974-9605, e-mail saripp@utk.edu.
Joint Appointment
Micro-sized implantable sensors are poised to revolutionize orthopedic medicine by helping surgeons detect infection or materials failure in replacement joints.
Information about infection or failure due to wear and tear in joint replacements is currently available only through standard X-ray and clinical examinations. Despite antibiotic use and sterile operating room practices, infections can occur, causing the patient significant pain, says Mohammed Mahfouz, a professor in the University of Tennessee's Department of Mechanical, Aerospace, and Biomedical Engineering and co-director of the Center for Musculoskeletal Research (CMR). In such cases, the implant usually has to be removed, resulting in more bone loss and increased recovery time for the patient.
Microsensors embedded in "smart" joints, however, offer solutions to both types of implant failure through early detection of infection and potential materials failure. Sensors that monitor chemical changes occurring inside the joint signal the onset of infection earlier than ever before, explains Emily Pritchard, a CMR research assistant. Meanwhile, pressure sensors examine how well the joint is operating and holding up during such activities as climbing stairs or performing deep knee bends.
The data from inside the joint is transmitted wirelessly to a computer at the clinic or a hand-held device, providing doctors with feedback on a patient's status at intervals following surgery. In this way, "if a doctor perceives any problems, he can take action to prevent the spread of infection or recommend customized physical therapy to stave off a revision due to wear before the patient has to go through a lot of pain," Pritchard notes.
The pressure sensors are already being tested, whereas the chemical sensors are still in the prototype stage, according to Pritchard. Both types of sensors are designed for use in any artificial joint, and the chemical sensor could be useful in any type of invasive surgery where infection is a concern.
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For more information, contact Mohammed Mahfouz at the Center for Musculoskeletal Research, (865) 974-2093, or e-mail mmahfouz@utk.edu.