Published 5 October 2021 at 17.45
Domestic. Researchers at Chalmers University of Technology have created microscopic vehicles that can be controlled using the power of light. By pointing a light source at small specially prepared particles – metaphores – the researchers have succeeded in driving them in controlled paths. They have also got the craft to transport other particles.
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Light has an inherent power that can move microscopic objects. That discovery is the basis for the Nobel Prize-winning optical tweezers, where researchers were able to show how a focused laser beam can capture and hold particles with great precision.
Now a research group at Chalmers University of Technology and the University of Gothenburg has shown that the power of unfocused light, a so-called plane wave, can be used to control a microparticle in a controlled orbit. The research was recently presented in a scientific article in the journal Nature Nanotechnology.
The small vessels that the researchers have made are ten micrometers wide and one micrometer thick, ie only one thousandth of a millimeter. The minimal particles have been coated with an artificial material – a so-called meta surface. Metaytar consists of carefully designed and interplayed nanoparticles that have been tailored to control light in unusual and innovative ways.
In the future, it is hoped to be able to use meta-surfaces in, among other things, cameras, microscopes, electronic screens and other technology gadgets that require advanced optical components. Meta surfaces are usually seen as stationary objects that can control and influence light. But in this case, the research team chose to turn the matter around and instead use how the power from the light affects the meta surface itself.
The researchers placed the microscopic particles – the metaphores – in the bottom of a water-filled container and illuminated them with laser light. Through a purely mechanical process, which takes place independently of the heat generated by light, scientists were able to control the movement and speed of metaphores with great precision and even steer them in different directions and in different formations by varying the polarization of laser light.
< p>– According to Newton's third law, there is an equal and opposite reaction to every event. In this case, it means that when the light reaches the meta surface, it deviates in a new direction, and the reaction force causes the microscopic vessel to move in the opposite direction. It's like playing billiards and two balls hitting each other and going in different directions. You can compare the meta surface and the light, the photons, to two billiard balls that collide with each other, says Mikael Käll, professor at the Department of Physics at Chalmers University of Technology and responsible for the research project, in a mailing.
– The meta-vessels are stable, and we can navigate them in a predictable and controllable way. With advanced automatic feedback systems and more sophisticated control of the intensity and polarization of the light source, even more complex navigation could be possible, says Daniel Andrén, former doctoral student at the Department of Physics and first author of the article.
Researchers could also use the metaphors as conveyors by making them put small particles in front of them in the water tank. They could easily move, among other things, microscopic plastic particles and yeast cells. The metaphorical vessel even managed to move a grain of dust 15 times larger than itself.
– In the exploration of optical forces, there are many interesting effects that are not yet fully understood. It is not applications that drive this type of research, but to explore different possibilities. In a number of different stages ahead, you never know what will happen. But the fact that we show that you can use the particles to move other things, indicates a possible application of them as transporters for other objects, for example in cell solutions, says Mikael Käll.