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SIUC researcher could revolutionize explosive detection

by ashley wiehle, the southern

Tuesday, May 29, 2007 7:04 AM CDT

CARBONDALE - Ling Zang's work hangs on the walls of Neckers Hall at Southern Illinois University Carbondale like blazing pieces of modern art.

Intricate strands of nanowires, magnified hundreds of times, are cobweb images not of art but of an exact science so ground-breaking it could revolutionize the detection of explosive substances.

Zang, an assistant professor in the Chemistry and Biochemistry Department, has been working for two years on his research, which recently was featured in the Journal of American Chemical Society.

His work has not gone unnoticed. Zang is the recent recipient of a National Science Foundation grant worth $592,000, just one of a string of grants that has allowed Zang and his group to continue their work.

Understanding the power of molecules and their abilities when clustered together in long strands known as nanowires could create a superior means to detect explosive devices such as bombs and landmines.

Traditional forms of detection are specially trained dogs and electronic sensors, such as what one would walk through for an airport security screening.

Screening explosives relies on trace amounts of vapor.

"A bomb is solid, but you still have a very small amount of vapor," Zang said, explaining that bombs give off a vapor of five parts per billion.

Although effective, airport screening systems aren't portable, and they aren't nearly as sensitive as nanofibers. A typical electronic sensor can detect vapors at 100 parts per trillion.

However, a strand of Zang's molecules can detect explosive vapors in almost nonexistent proportions - 10 parts per trillion, to be exact.

That's 10 units of explosive material versus 1,000,000,000,000 units of air.

It is believed that dogs' ability to detect scents rivals that of a molecule, but dogs suffer from a fallibility that molecules do not.

Molecules, after all, don't need a drink - or a bathroom break.

"Dogs do better than the electronic sensor, but they are very expensive to train," Zang said. "The dog also gets tired. One dog cannot work a long time. He gets tired and he loses sensitivity."

A strand of multi-functional molecules clustered together in a nanowire can create a series of reactions that accurately detect tiny traces of explosives.

When stacked together - Zang compared them to dinner plates - the molecules can feed off one another's reaction. A molecule at the end of a strand is excited by ultraviolet light, and soon molecules throughout the chain are similarly excited.

The excited molecules will conduct light from one end to the other, unless an explosive such as TNT is present.

Explosives such as TNT act as "quenchers," Zang said. A solid grid of nanowires will be snuffed out by the presence of TNT and light cannot be conducted from one end of the chain to another.

"If you have TNT as a quencher, you don't have emission," Zang said.

Zang has been joined in research by four graduate students, a post-doctoral student and three joint graduate students he shares with other researchers. He partners with Jeffrey Moore, an organic chemist at the University of Illinois.

Moore creates special molecules, which Zang uses to create nanowires.

Although one typically thinks of airport searches when hearing reference to bombs, the ability to use molecules can have a major impact on land mines.

About 120 million landmines are still scattered across the world, Zang said. It would cost an estimated $1,000 per mine to recover each, and it is difficult work. Landmines are buried underground and have much fainter vapors that are significantly harder to detect.

Based on work performed in the laboratory, Zang believes his nanowires could easily detect landmines.

"These are just projections," Zang said. "We cannot access any landmines at the moment."

Nanowires are proving to be useful in different media, Zang said. Another set of experiments he's been working on uses the current of nanowires to detect poisons such as hydrazine.

ashley.wiehle@thesouthern.com

529-5454 ext. 5816