Trapping Center Controls Spin Direction

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.