Japanese Researchers Design Linear Nanomotors Controlled Using Light

Researchers from the Institute of Industrial Science, University of Tokyo, have designed linear nanomotors that can move in controlled directions using light. Researchers say that the work opens the door for new microfluidics, including lab-on-a-chip systems with optically actuated pumps and valves. The researchers point out that powering and controlling a motor smaller than a single bacterium precisely is very difficult.The researchers developed a system of linear motors made from gold nanorods that can move in a controlled direction with exposure to laser light. The nanomotors aren't constrained to the direction of the light alone. They can move similarly to how a sailboat can move in any direction by adjusting its rigging. The nanomotors can move based on their orientation when exposed to a laser beam traveling from another angle.

Motion is powered by the lateral optical force created from the sideways scattering of light. The need to focus and shape the laser with lenses, which is a difficult task, is eliminated. Motor sizes also are constrained by the wavelength of light, which was an issue with previous devices. The first author of the research paper Yoshio Tanaka said that instead of being limited to moving in the direction of the laser light or the field gradient, the direction is determined by the orientation of the nanoparticles themselves.

The directional scattering is used to propel the nanomotor thanks to the careful design of the separation between the nanorods. That design allows constructive interference in one direction and destructive interference in the other to propel the device. The team's new platform features moving parts that follow predetermined paths nudged along by unfocused light.

The design will significantly reduce the cost and complexity of this type of device while improving precision and reliability. It's not clear when the technology may be commercialized.