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All These Micromotors Need Is Light

We've all seen those pictures of cogs and gears just millionths of a inch across. And predictions that tiny machines will one day move through the body dispensing drugs or performing other tasks in the microworld have become commonplace (see BW Online, 12/7/00, "These Minuscule Motors May Herald a New Medical Era"). But the researchers turning out the parts to make tiny devices face a major challenge -- finding ways to power microscopic pumps and propulsion systems.

One answer, it seems, may lie in the beams of laser light. A team headed by Pal Ormos at the Hungarian Academy of Sciences has built structures that rotate like windmills from the energy in them.

Ormos and his graduate student, Peter Galajda were conducting research with "optical tweezers" -- devices that trap and immobilize atoms and other tiny objects in laser beams so they can be studied under a microscope. They noticed that the microscopic beads they were studying sometimes began to rotate when they were illuminated by a laser beam. They wondered if the force of light might be strong enough to power micromachines. "We decided to see if we could make it work," says Galajda.

Top: Computer rendering. Bottom: Electron micrograph of the

real thing, 3 microns in diameter

Credit: Pal Ormos and Peter Galajda

TURNING COGWHEELS. To test the idea, the microtechnologists used lasers to fashion plastic into a variety of candidate shapes, including helixes and propellers. One, which looks like an ordinary lawn sprinkler spins at several revolutions per second when illuminated by a 20-milliwatt laser beam. In a recent issue of Applied Physics Letters, the researchers described using light to turn a series of cogwheels that were each only 5 microns in diameter.

Because the devices have to be illuminated, applications inside the body are ruled out. But Galajda sees plenty of potential for light-powered micromachines. In their next step, the team plans to build a tiny system in which the micromotors work as miniature pumps and switches. These could be incorporated into "labs on a chip," which are used to analyze chemicals and DNA as well as in medical diagnosis.

Another promising use may be the measurement of fluids' viscosity and other properties in microscopic environments. Moreover, fixing a rotor to the end of molecules such as proteins or DNA and applying a twisting force may help scientists understand how molecules fold and their mechanical properties.

The researchers caution that all they have accomplished so far is proving the principle. But it's likely that their tilting at windmills will turn out to have been a very bright idea. By Alan Hall in New York

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