Sensor Traces DIY Bombs
SAN DIEGO, March 21, 2008 -- A penny-sized electronic sensor is capable of sniffing out hydrogen peroxide vapor in the parts-per-billion range from peroxide-based homemade explosives, such as those used in the 2005 bombing of the London transit system.
The sensor, developed at the University of California, San Diego (UCSD) could also have widespread applications in improving the health of factory workers by providing a new tool to inexpensively monitor the toxic hydrogen peroxide vapors from bleached pulp and other products to which they're exposed.
"The detection capability of this tiny electronic sensor is comparable to current instruments, which are large, bulky and cost thousands of dollars each," said William Trogler, a chemistry and biochemistry professor at UCSD and one of its inventors. "If this device were mass produced, it's not inconceivable that it could be made for less than a dollar."
The device was invented by a team led by Trogler; Andrew Kummel, a chemistry and biochemistry professor, and Ivan Schuller, a physics professor. Much of the work was done by UCSD chemistry and physics graduate students Forest Bohrer, Corneliu Colesniuc and Jeongwon Park.
The sensor works by monitoring the variability of electrical conductivity through thin films of "metal phthalocyanines." When exposed to most oxidizing agents, such as chlorine, these metal films show an increase in electrical current, while reducing agents have the opposite effect -- a decrease of electrical current. But when exposed to hydrogen peroxide, an oxidant, the metal phthalocyanine films behave differently, depending on the type of metal used. Films made of cobalt phthalocyanine show decreases in current, while those made from copper or nickel show increases in current.
The UCSD team used this unusual trait to build the sensor. It is composed of thin films of both cobalt phthalocyanine and copper phthalocyanine to display a unique signature whenever tiny amounts of hydrogen peroxide are present, UCSD said in a statement.
Bombs constructed with hydrogen peroxide killed more than 50 people and injured 700 more on two London subway trains and a transit bus during rush hour on July 7, 2005. More than 1500 pounds of a hydrogen peroxide-based mixture was discovered after an alleged bomb plot in Germany that resulted in tthree arrests in September.
Trogler said that because the team's sensor is so little affected by water vapor, it can be used in industrial and practical applications. The university has applied for a patent on the invention, which has not yet been licensed.
Funding for the research study was provided by the Air Force Office of Scientific Research. The team's findings are published in this week's Journal of the American Chemical Society.
For more information, visit: http://ucsd.edu
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