In continuing work on the development of optically driven micromotors, physicists at Kyoto University in Japan have demonstrated that the location of the trapping center determines the direction of rotation of a chiral object. They reported their findings in the Dec. 16 issue of Applied Physics Letters.The scientists exposed chromosomes from African clawed frog sperm to the focused 1064-nm output of an Nd:YAG laser. They observed that the location of a 2-µm-diameter polystyrene bead on the helical molecules determined whether they rotated clockwise or counterclockwise around the light axis and that the laser power determined their angular velocity.