Laser-Powered Nanomotors Follow Their Path

Researchers from the Institute of Industrial Science at the University of Tokyo have designed linear nanomotors that can be made to move in controlled directions by laser light. The technology has applications in microfluidics, including lab-on-a-chip systems with optically actuated pumps and valves, and the researchers envision using the technology to develop a new platform for nano-size machinery with moving parts that follow predetermined paths while being propelled by unfocused light.

The technology could ultimately reduce the cost and complexity of such devices while improving precision and reliability.

The system consists of linear motors made from gold nanorods that move directionally according to their orientation upon being exposed to laser light. When exposed to beams traveling from different angles, the nanomotors move according to their orientation. The lateral optical force created from the sideways scattering of light powers this motion, removing the need to focus or shape the laser beam with lenses.

The sizes of the motor(s) are additionally not dependent upon the wavelength of light, as is the case with previous and similar versions of motor devices. The technology instead relies on localized surface plasmon resonance — collective oscillations of free electrons — within periodic nanorod arrays that produce scattered light in a particular direction.

“Instead of being limited to moving in the direction of laser light or the field gradient, the direction is determined by the orientation of the nanoparticles themselves, said Yoshito Tanaka, first author of the paper describing the research.

“Careful design of the separation between nanorods leads to constructive interference in one direction and destructive interference in the other. This allows us to produce directional scattering to propel the nanomotor,” said Tsutomu Shimura, professor of applied nonlinear optics at the University of Tokyo.

The research was published in Science Advances (www.doi.org/10.1126/sciadv.abc3726).