Sweating the small stuff Home

Light and a Single Molecule Combine to Make a Machine
By Guy Gugliotta
Washington Post Staff Writer

Scientists have for the first time used the power of light to create mechanical energy for a microdevice, making a single molecule of plastic drive a tiny machine.

The experiment could have important implications for the field of nanotechnology, which seeks to miniaturize machines and mechanisms to an atomic or molecular scale. "We know [the machine] works pretty well," said researcher Hermann E. Gaub. "Miniaturization drives progress."

Gaub, a physicist at the University of Munich's Nanoscience Center, was part of a German-led team that used well-known materials in a relatively simple experiment to turn light into mechanical energy, something that had never been done before on the molecular level. The results of their research were reported today in the journal Science.

The idea, Gaub said, was to demonstrate that light at a nanolevel could "interface with the outside world" to create a working device. The "outside world" in this case was bigger -- it was microscopic.

The device was a spring, shaped like a miniature silicon diving board, hanging over a sheet of glass. Attached to the bottom of the diving end of the board was one end of a single long molecule of a plastic called azobenzene. The other end of the molecule hung down from the bottom of the diving board and was attached to the glass.

Gaub said azobenzene is well known for its kinkiness -- it looks like a length of knotted telephone cord when it hangs vertically. It is also known to extend or contract when different light frequencies change the configuration of the atoms within the molecule.

By shining one frequency of light on the device, the team was able to crimp the molecule, causing it to pull the diving board downward -- converting light into mechanical energy. When another light frequency was used, the molecule relaxed.

"That's pretty much the heart of it," Gaub said. "We could put a weight on the spring [diving board] and use it to move the weight." He likened the device to a piston in an automobile engine, where the molecule of plastic is the gasoline, activated by the light. ."We shine light and it moves."

In the world of the very small, practical applications for light-driven engines are not yet abundant. As scientists seek to go from the merely microscopic to the atomic and molecular, the properties of different materials can change markedly, and simply building a nanodevice is an exercise in innovation.

But at the next level up -- micromachines -- devices are in many cases much more recognizable, with tiny interlockings of silicon gears and levers driven by electronic microcircuitry.

"In the world of micromachines, there's not really a need to get a new motor," said Paul McWhorter, chief technology officer for MEMX, a microtechnology firm based in Albuquerque. "We build microscopic circuits, apply voltages and cause things to move.

"But if you think broader in terms of a new tool for interacting with light, or a new tool that interacts at a specific wavelength, that's different," McWhorter said. "That's very interesting and exciting."

Gaub said his plastic molecule will have eventual applications in nanotechnology, but right now can contribute to advances in the micro-world. He noted that many sensors and other tools of chemical analysis are getting smaller and smaller and "will require little valves and little machines."

His molecule could provide the driver: "It would look a lot like the device we made," Gaub said. "The bar could be part of the valve that closes or opens. Shine light on the valve and it would open. Change the frequency and it would close."

The devices could also be hooked together to make chains of light-driven switches, sidestepping the need for circuitry. "You have to wire circuits," Gaub said. "Shining light on something is more straightforward."

Gaub acknowledged, however, that his molecular device is not ready for the marketplace. The chief impediment is that the molecule breaks after the experiment runs for a day.

"There is room for improvement," Gaub said. "We can try different molecules that are less susceptible to optical damage. There are different environments we can try to get longer life. It will be interesting to work out the details, but for now we are just happy that it worked."