An extremely sensitive and selective sensor that can detect minute traces of the chemical nerve agents sarin and soman has been successfully tested by researchers at Johns Hopkins University. Sarin was the agent used in the infamous 1995 terrorist attack on a Tokyo subway. Both compounds are reputed chemical weapons in the arsenals of some countries.
The sensor is described in the January 15 print edition of the peer reviewed journal Analytical Chemistry, published by the American Chemical Society, the world's largest scientific society. The web edition of the article was published Dec. 10.
The sensor, which combines molecular imprinting with optical luminescence, is able to detect sarin and soman in water at levels as low as 600 parts per quadrillion. "It's a million times more sensitive than other reported solution sensitivities," says George Murray, Ph.D., a senior research chemist with Johns Hopkins' Advanced Physics Laboratory in Laurel, Md. "Just a thousand molecules probably is all it would take for us to detect it," he claims. "That's smaller than a gnat in a bathtub of water."
Molecular imprinting is analogous to making a plaster impression of the particular molecule you want to find, says Murray. "The cast is made of a stiff plastic so that when the molecule is removed, the shape of the molecule in the cast is preserved." Because the structure of each molecule is unique, the probe only recognizes the specific molecule for which you are probing.
The actual probe developed by Murray and his colleagues for detecting nerve agents in water is a tapered optical fiber, which is treated with europium, a metallic element used in the manufacturer of television screens. The fiber is hooked to a spectrometer and a light source. Light is directed to the end of the fiber in the solution being examined and the light that returns from the tip is analyzed by the spectrometer.