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17 Jun 2002
Hungarian researchers succeed in controlling the rotation of micromachines that are powered by light.
Researchers in Hungary have succeeded in reversing the rotation of a micro-rotor trapped in optical tweezers. The team says that their light-driven rotors are destined to find applications in areas such as biotechnology. (Applied Physics Letters to appear)
The crucial element of this system is an oil-immersed objective lens with a very high numerical aperture. Changing the position of the objective lens controls the direction of rotation.
"The rotor can assume two stable axial positions in the trap," explains lead researcher Pál Ormos from the Hungarian Academy of Sciences. "One equilibrium position exists when the rotor is closer to the objective than the center of the trap. In this case we see anticlockwise rotation. Moving the objective lens away from the sample pushes the rotor beyond the focus and we see clockwise rotation."
Ormos and co-workers use an inverted optical tweezers configuration. An objective lens with a numerical aperture of 1.4 focuses the output from an infrared diode laser emitting at 994 nm to form the tweezers.
The trapping intensity is approximately 20 mW. "We found that the rate of rotation is linearly proportional to the laser intensity," said Ormos. "For 20 mW, the frequency is 2 Hz."
A two-photon polymerization method is used to fabricate the rotors. Polymerization of a UV-curable adhesive results in a glass like material. Pointlike polymerization is achieved by focusing the 514 nm line of an argon-ion laser on the adhesive.
The team now hopes to make complex integrated systems where all the components of a micromechanical system are integrated. Ormos says this could find applications such as measuring the properties of large biological molecules and making components such as miniature pumps and actuators for lab-on-a-chip devices.
"We would also like to commercialize this system," says Ormos. "But this takes time as we have to patent things before publishing."
Author
Jacqueline Hewett is news reporter on Optics.org and Opto & Laser Europe magazine.
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