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In 1995, members of the religious sect Aum Shinrikyo unleashed an impure form of sarin gas on several trains of the Tokyo Metro subway during rush hour, killing 12 people and severely injuring more than 1,000. To date, these coordinated attacks are the deadliest in Japan since the end of World War II.
Sarin is an extremely poisonous, colorless and odorless compound discovered in the 1930s and later adapted for use in chemical warfare. It is liquid at room temperature but readily turns to gas. Sarin belongs to a class of weapons known as nerve agents, which includes tabun, soman and VX. As the name suggests, nerve agents target a person’s nervous system. Victims exposed to them suffer severe, uncontrolled muscular spasms and convulsions and eventual death by asphyxiation.
Assoc. Prof. Sanjeev Manohar, director of UML’s Green Technology Laboratory, recently received a two-year, $300,000 research grant from Advanced Concepts and Technologies Inc., a defense firm based in Waco, Texas, to develop an engineering prototype device for detecting sarin and other nerve agents using thin-film, carbon-nanotube sensors. Manohar also received $100,000 to purchase instruments for use by UML and Advanced Concepts and Technologies. This collaboration is in support of a military program of the Edgewood Chemical Biological Center for the U.S. Department of Defense.
“Carbon nanotubes are microscopic structures measuring only a billionth of a meter in size,” says Manohar. “Visually, they look like black, sooty powder, much like very fine charcoal. They’re another form of pure carbon.” He says one way to picture a carbon nanotube is to imagine chicken wire made of pure carbon that is rolled in the form of a long, spaghetti-like cylinder.
Manohar and researchers at Advanced Concepts and Technologies made a very thin layer of these nanotubes on the surface of an ordinary, lightweight plastic transparency film and measured the nanotubes’ electrical resistance continuously with time. “We found that the resistance changes significantly when the film is exposed to common toxic organic vapors, and very dramatically when exposed to simulants for nerve agents,” he explains. “When these vapors are removed, the resistance comes back to its original value, forming the basis of a detector/sensor for chemical threats.”
Unlike many existing sensing materials, carbon nanotubes are chemically and environmentally very stable. “Our sensors, which are about the size of a thumbnail, can be bent or folded without losing their electrical conductivity, which makes them ideal for use in rugged, hostile terrains such as battlefields,” he says.
UMass Lowell will develop a low-cost sensor array that can be integrated into a detection module or suite of modules the size of a credit card and will be self-contained, durable and simple to use. “Due to its small size, light weight, and minimal expense, carbon-nanotube sensors can be designed and used as stand-alone, handheld, portable systems for soldiers in the frontlines or integrated into military vehicles and aircraft to provide constant monitoring of the air along their paths,” he says.
“At the moment, I’m the sole UML faculty on this project, but I do plan to bring in experts in the areas of pattern recognition and signal processing,” says Manohar. He hopes to expand his research and develop sensor arrays that would detect not only nerve agents but also other chemical agents, such as mustard gas, chlorine and phosgene, as well as biological agents, such as anthrax, ebola and cholera.
Manohar believes they can readily adapt the carbon-nanotube detector for civilian use. “For example, it can be used to detect soil and groundwater contamination from heavy metals and organo-phosphate fertilizers and pesticides, though much work still needs to be done in this area,” he says.