Optically driven rotors

The advances in optically controlled micromanipulation are continuing at a rapid pace. A recent paper published in Applied Physics Letters describes an optically-driven rotor^†, which could be the precursor to nanopumps, miniature mechanical pumps that could drive suspended particles around circuits in microfluidic applications.

Ship in a Bottle

The entire device, which comprised the rotor and the cavity in which it was confined, was carved out of a glass substrate using femtosecond laser etching in conjunction with more conventional chemical etching. The tiny glass rotor was etched into a four-wing shape separate from the glass cavity, like a model ship trapped inside a bottle.

The cavity around the rotor was filled with water, allowing the rotor to spin freely when exposed to a focused beam of light from a Nd:YAG laser operating in the near infra-red. Rotation resulted from the shape of the rotor, with the direction being dependent on whether the light was incident from the front or the rear of the device. It was shown that the torque responsible for rotation was due to light reflected or refracted from the sides of the rotor, and that the speed of rotation was proportional to the incident laser power. Maximum speeds of approximately 100 rpm were recorded.

Although no specific function was demonstrated, these little rotors could be the precursor to applications in which similar devices act as miniature pumps or mixers in microfluidic circuits. Perhaps it would even be possible to drive tiny probes carrying payloads within biological systems, ensuring they reach their target under the influence of a driving light beam.

† Laser microfabrication and rotation of ship-in-a-bottle optical rotators
Shigeki Matsuo, Satoshi Kiyama, Yoshinori Shichijo, Takuro Tomita, Shuichi Hashimoto, Yoichiroh Hosokawa, and Hiroshi Masuhara, Appl. Phys. Lett. 93, 051107 (2008), DOI:10.1063/1.2967872