College of LAS « Illinois


Chemists Solve Century-Long Puzzle About How to Study Single Molecules

Absorption spectroscopy offers new level of precision to scientists.


University of Illinois scientists have found a way to use an old, trusted technique to do something dramatically new—study the properties of a single molecule. In doing so, they solved a century–long puzzle.

For more than 100 years, researchers have studied molecules using two primary types of spectroscopy, says Martin Gruebele, a chemist in LAS who is leading the project along with Joe Lyding in electrical and computer engineering. However, for years these methods could detect only large numbers of molecules at a time.

About 10 years ago, scientists finally came up with a way to use "fluorescence spectroscopy" to study single molecules. But scientists had not figured out how to use "absorption spectroscopy" to study single molecules—until now. Gruebele and Lyding's team culminated five years of research with their discovery of how to detect single molecules using absorption spectroscopy, an advance that offers a new level of precision to scientists.

With absorption spectroscopy, scientists shine a beam of light on a molecule. The trick is to detect when the molecule absorbs a small portion of the billions of photons, or particles of light. It's a little bit like being able to detect when a handful of sand has suddenly vanished from a beach.

The absorption of these photons tells researchers important information about that specific molecule. Researchers can then use this information for a myriad of uses, such as designing microscopic, "nano–sized" electronic devices.

"What we came up with is a way to literally ‘feel' the absorption of the photons by the molecule," Gruebele says. In other words, his team looked for changes in the molecule itself, which would indicate whether it had absorbed the photons. The U. of I. team detected these changes using a unique series of technical tricks.

"People had tried some of these techniques before," Gruebele says. "But they had never put them all together in the right way. The devil is in the details."

Fall/Winter 2006–07