Next on CSI: Surface-enhanced Raman spectroscopy

New twist on powerful analytic method makes it much more useful

Scientists have developed a quick and dusty method for detecting trace quantities of unknown substances.

Described in the March 18 Nature, the new technique amounts to little more than sprinkling a layer of gold dust on the surface to be tested. Yet it will soon make one of science’s most powerful but unwieldy chemical analysis methods useful for detecting trace amounts of materials such as explosives, drugs and environmental contaminants, the researchers who invented it say.

“This really does make the possibility of detecting things … very, very practical, says physical chemist Martin Moskovits of the University of California, Santa Barbara, who wrote a commentary on the research in the same issue of Nature. The new method could have broad applications, from forensics to food inspection, says Moskovits. “It potentially allows you to do in situ analysis at a much greater level of sensitivity.”

The researchers, led by Jian Feng Li of Xiamen University in China, call their new method shell-isolated nanoparticle-enhanced Raman spectroscopy, or SHINERS for short. They tested it by identifying minute amounts of hydrogen on a one-crystal silicon wafer, probing the surfaces of yeast cells and detecting the insecticide parathion on an orange peel.

The new research is a variation on the technique known as surface-enhanced Raman spectroscopy, which shines a laser on a substance sitting on a specially prepared surface and then analyzes interactions between the laser light and the molecules in the substance.

The research team tipped this method on its head. Traditional surface-enhanced Raman spectroscopy relies on the nooks and crannies of a specialized surface to concentrate the light energy emitted by the sample. But the new method lays this specialized light-concentrating surface on top of the sample, in the form of a “smart dust” of tiny gold nanoparticles coated with a thin inert shell containing silicon or aluminum. When laser light strikes the gold nanoparticles, “hot spots” of emitted energy are created between the nanoparticles and the sample that can be analyzed spectrographically.

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