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Tokyo, Japan – Researchers at the University of Tokyo Institute of Industrial Sciences (UTokyo-IIS) have designed novel linear nanomotors that can be moved in controlled directions using light. This work paves the way for new microfluidics, including lab-on-a-chip systems with optically driven pumps and valves.
The world of nano-scale machines looks very different from what the contraptions we have become used to. For example, precisely powering and controlling an engine smaller than a single bacterium can be much more difficult than, for example, driving a car.
Now, a team of scientists led by UTokyo-IIS has introduced a system of linear motors made with gold nanotubes that can move in a controlled direction when exposed to laser light. Like a sailboat that can move in any desired direction by adjusting the rigging, these nanomotors are not bound to follow the direction of the light. Rather, they move according to their orientation even when exposed to a laser beam traveling from another angle.
The movement is powered by the lateral optical force created by the lateral scattering of light from the particles. As a result, the need to focus or shape the laser beam with lenses, which was once a difficult task, is eliminated. Furthermore, the size of the motor is not constrained by the wavelength of light, unlike previous devices.
“Instead of just moving in the direction of the laser light or the gradient field, the direction is determined by the orientation of the nanoparticles themselves,” says lead author Yoshito Tanaka. The key to this technology is localized surface plasmon resonance – collective oscillations of free electrons – within periodic arrays of nanotubes. These can produce diffused light in a particular direction. “Careful design of the separation between nanotubes leads to constructive interference in one direction and destructive in the other. This allows us to produce directional dispersion to propel the nanomotor,” says senior author Tsutomu Shimura.
The researchers envision using this technology to create a new platform for nano-sized machinery with moving parts that follow predetermined paths as they are pushed by blurry light. This will greatly reduce the cost and complexity of these devices while also improving accuracy and reliability.
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The work is published in Advances in science as a “plasmonic linear nanomotor employing lateral optical forces” (DOI: 10.1126 / sciadv.abc3726).
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