For microscopic swimmers, paddling is hard because at such tiny lengths, water seems as thick as honey. To get around this viscosity, scientists from the University of Sheffield in England and their colleagues have developed plastic swimmers without moving parts. They coated 1.6-micron-wide balls on one side with a thin layer of platinum and dropped them in a solution of hydrogen peroxide and water. The metal catalyzes the breakdown of hydrogen peroxide into oxygen and water, propelling the balls at speeds up to five microns per second, half as fast as similarly sized bacteria move. After a few seconds, the balls start to jostle with surrounding atoms and molecules and then meander, but the designers suggest that magnetic fields could guide the swimmers. They could also adapt them to work in fluids such as blood, to help deliver drugs within the body. Wade into the findings in the July 27 Physical Review Letters.
This article was originally published with the title "Paddle-Free Swimming" in Scientific American 297, 4, 36 (October 2007)