Nanoscale robots that roam the bloodstream and attack molecular invaders are still fantasy. Mobile powered nanodevices, however, look more likely to become as reality thanks to a new trick for operating and even steering tiny rods and gears with chemical energy. The advances lay the groundwork for nanoscale cargo movers and more complex motors.
Finding ways to power tiny devices has long been among nanotechnologists' greatest challenges and most popular pursuits. Numerous teams have borrowed proteins such as ATP synthase that use chemical energy to generate motion. But proteins are fragile, raising questions about how useful such devices would be in the nanomechanical world.
Last year, a Pennsylvania State University, University Park, team led by chemist Ayusman Sen reported a more robust alternative. They used the catalytic activity of platinum to propel tiny gold rods. In an aqueous solution, the platinum-tipped rods continuously converted hydrogen peroxide into oxygen and water. The oxygen-rich region lowered the surface tension between the tips of the rod and the liquid. Because the rest of the gold rod was attracted to the region of the low surface tension, the rod moved in that direction, generating more oxygen as it went. The only trouble with this approach was that the rods zigzagged like drunken sailors.
So for their current work, reported in the advance online version of Angewandte Chemie International Edition, Sen and his colleagues gave the rods some direction by adding nickel stripes. When magnetized, these stripes orient the rods perpendicularly to an externally applied magnetic field. So by simply moving a magnet, the researchers could steer their rods. For an encore, the group reports in the February issue of Small that they fashioned tiny metal gears in which each tooth is coated on one side with platinum. The teeth then all work together to push the gear through the water, spinning the gear.
Chad Mirkin, a nanotechnology expert at Northwestern University in Evanston, Illinois, calls the new work "a spectacular demonstration of how you can use chemistry to manipulate nanostructures in a whole new way." Sen says that his group is already working on making sensors that swim through fluids to find their target molecules and complex interlocking gears driven by catalysis.