Tiny, Light-Driven Gears Could Lead to Solar-Powered Micromachines

Researchers from the University of Rome and the Italian Institute of Technology in Genova have demonstrated that pinwheel-shaped microgears floating on a liquid surface can rotate at speeds of up to 300 rpm when illuminated by an ordinary LED. This light-driven motion, which arises because the light creates a tiny temperature difference and, subsequently, a surface tension difference in the surrounding fluid, is about five orders of magnitude more efficient than other mechanisms that convert light into work. Because the effect is not size-dependent, the scientists expect that the system could be scaled to both the macroscale and the nanoscale. The researchers fabricated the microgears using laser lithography and coated them with a layer of amorphous carbon to increase light absorption. While previous light-driven motors generally require high-power laser beams to induce motion, here the wide-field LED could induce motion with just a few microwatts of power per gear, corresponding to a 100,000 times higher light-to-work conversion efficiency. "Future research in this direction could lead to the development of micromachines that are capable of transporting tiny loads, such as individual cells, within miniaturized devices powered by the simple exposure to sunlight," says Roberto Di Leonardo at the Italian National Research Council, and the team coordinator.