Light powers biochip gears

In the microscopic world, a beam of light carries enough force to move objects.

Researchers from St. Andrews University in Scotland have fashioned a type of microgear with center slots that pick up the rotational momentum from light, allowing the gears to rotate when illuminated by a type of polarized light.

The devices could eventually be used to pump and mix extremely small amounts of chemicals. The system of slots and polarized light could also be used to make a diverse array of mechanical parts that can be rotated or aligned using light, according to the researchers.

The slots change the amount that light bends as it enters the gear, depending on its polarization. Light is polarized when its electric field vibrates in one direction along the plane perpendicular to the direction of the beam. Linearly polarized light that is oriented along the slots bends more than light oriented across the slots. Light that bends more applies a greater lateral force to the gear, causing the gear to line up with the light's polarization.

When circularly polarized light strikes the parallel slots in the gear, the light's rotational momentum is transferred to the gear. The stronger the light beam, the faster the rotation.

Devices that use the gear system could become practical within five years, according to the researchers. The work appeared in the June 19, 2005 issue of Nature Materials (All-Optical Control of Microfluidics Components using form Birefringence).