It’s tantalizing to think about the future of vehicles; whether they go the route of sustainability and reach maximum efficiency with electricity as its power source, or just go plain fast and zoom past land speed records—these mechanical marvels are pushing what we know about motion and engineering to its absolute limit. As such, we often hear about these vehicles going “bigger,” in both scale and impact.
It comes as a surprise, then, when scientists choose to look the other way, and see what we can do in the other direction. It appears that this is exactly what the scientists back at Chalmers University of Technology (CUT) in Gothenburg, Sweden, did; in a recent study these scientists published in the journal Nature Nanotechnology, the research team—led by CUT Department of Physics professor Mikael Käll—pushed our understanding of locomotion towards the opposite end of the size spectrum, and went for really, really tiny speedsters they called “metavehicles.”
These “metavehicles” thay they developed take advantage of the fact that light, at the microscopic level, can cause objects to move. In essence, light at this scale pushes things much like how billiard balls hit each other in a pool table; hit a particle with enough energy and it should move in the same direction that you hit it towards. This very concept is what brought Arthur Ashkin his Nobel Prize in Physics back in 2018: he co-opted light to create what he and his team called “optical tweezers” that can grab single atoms, viruses, and single living cells.
Now, the team at Chalmers took advantage of this property of light to create their really tiny tow trucks. The entire “vehicle” is just a measly 10 microns wide and 1 micron thick; that’s one-thousandths of a millimeter—just a bit more than half the size of a single bacterium.
They created these metavehicles by coating tiny particles with a material they call a “metasurface,” which themselves are made with very tiny arrangements of nanoparticles designed to “direct light in interesting and unusual ways.” Given their propensity for optical applications in technologies like cameras and optical equipment, one would think these special materials are stationary in nature. Käll and team, however, decided to think outside the box.
In their experiment, the research team placed these newly-developed metavehicles onto a dish covered with shallow water. Afterwards, they used loosely-focused laser light to direct what is called a plane wave of light onto the light-sensitive metavehicles. In doing so, they discovered that they can easily direct where these tiny vehicles would go just by adjusting the intensity and polarization of the laser light, much like how sailboats use the wind to push themselves along the sea.
Käll added: “According to Newton’s third law, for every action there is an equal and opposite reaction – this means that when the light hits the meta-surface, and is deflected in a new direction, the meta-surface is also pushed away in the other direction. […] Imagine playing pool, when two balls hit each other and bounce off in different directions. In this case, the photons and the meta surface are like those two pool balls.”
They also discovered that their new tiny vehicles can also essentially shuttle other nanoparticles along for the ride, just by placing these particles in front of the metavehicle. The team believes that practical applications for their novel technology are a ways off; however, they hope that their new technology may someday be used in similar applications, such as pushing necessary microparticles towards cells or through solutions.
(For similar small-scale explorations, check out our previous piece on “nanogenerator” wooden floorings that may power your next home.)
References
- Andrén, D., Baranov, D. G., Jones, S., Volpe, G., Verre, R., & Käll, M. (2021). Microscopic metavehicles powered and steered by embedded optical metasurfaces. Nature Nanotechnology, 16(9), 970–974. https://doi.org/10.1038/s41565-021-00941-0
- Coxworth, B. (2021, September 28). Microscopic metavehicles are pushed and steered by light. New Atlas. https://newatlas.com/science/microscopic-metavehicles-propelled-light/
- Nokia Bell Labs. (n.d.). 2018 Nobel Prize in Physics: Arthur Ashkin. Nokia Bell Labs. Retrieved October 13, 2021, from https://www.bell-labs.com/about/awards/2018-nobel-prize-physics/
