Self-propelled microparticles now able to move upstream

Science : Two teams of researchers have developed separate mechanisms that allow microscopic particles to move against the flow of liquid. The first team, from New York University, used a micrometer-sized plastic sphere with an exposed area of iron oxide. When placed in a hydrogen peroxide solution and activated by blue wavelengths of light, the iron oxide splits oxygen away from the hydrogen peroxide molecules. The resulting electrical gradient is strong enough to push the microparticles against the flow of the solution in a small capillary. The second team, from the University of California, San Diego, used a similar chemical reaction to increase the catalytic effect of an effort to produce hydrogen gas for fuel cells. In a solution of sodium borohydride, platinum reacts strongly, producing hydrogen gas. However, the platinum molecules are quickly covered in hydrogen bubbles, which slow then stop the reaction. So the researchers created a two-piece microparticle, half platinum and half titanium. Because the bubbles are produced on only half of the microparticle, the ejection of hydrogen gas from that side pushes the microparticle away, and the reaction can continue. The resulting process is 20 times more effective than simply reacting platinum with sodium borohydride.