New sensor chip to detect hydrogen peroxide in explosives

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A team of scientists at a US university has developed a tiny, inexpensive sensor chip capable of detecting traces of hydrogen peroxide, a chemical used in the most common form of homemade explosives.

The invention and operation of this penny-sized electronic sensor, capable of sniffing out hydrogen peroxide vapour in the parts-per-billion range from peroxide-based explosives, is detailed in a paper in this week's issue of the Journal of the American Chemical Society.

Besides, the sensor could have widespread applications in improving the health of industrial workers by providing a new tool to inexpensively monitor the toxic hydrogen peroxide vapours from bleached pulp and other products to which factory workers are 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 professor of chemistry and biochemistry at University of California, San Diego (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," he said.

The device was invented by a team led by Trogler, Andrew Kummel professor of chemistry and biochemistry and Ivan Schuller professor of physics.

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," they said.

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 their 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.

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 1,500 pounds of a hydrogen peroxide-based mixture was discovered after an alleged bomb plot in Germany that resulted in the widely publicised arrest last September of three people.