Controllable micromotors powered by near-infrared light could someday deliver drugs through a bloodstream or scoop up water pollutants. But without the buoyancy that liquid environments provide, micromotors have had a tough time fighting gravity.

Now, researchers in Canada have developed micrometer-scale micromotors that glide through the air on convection currents (Adv. Mater., doi:10.1002/adma.202505959). Scientists can steer the movements of the particles by changing the direction of the NIR light impinging on them.

Inspired by nature

In designing the spiky, round shape of the micromotors, the team at Concordia University drew inspiration from pollen particles, dandelion seeds and other natural objects that rely on air currents for transportation.

Starting with commercially available spherical zinc cores, the researchers synthesized a spiky layer of zinc oxide on the surfaces of the particles. This process increased the surface area of each particle by approximately 88%.

Next, the Concordia group transformed the spiked spheres into micromotors by adsorbing gold nanoparticles onto the ZnO surfaces. Finally, the researchers, as they wrote, “decorated” the micromotors with so-called up-conversion nanoparticles, which helped the team track the motions of the airborne spheroids.

Induced convection makes the micromotors—each with a diameter of roughly 12 μm—drift through the air like tiny gliders.

Gliding through air

Induced convection makes the micromotors—each with a diameter of roughly 12 μm—drift through the air like tiny gliders. Putting the spiked particles into a near-infrared laser beam (with a wavelength of: 808 nm) makes the gold specks on the ZnO surface heat up, thus warming the air around them. The additional heat creates small but significant convection currents that push the particles upward. Once the micromotors fly out of the beam and into a region of cooler air, they sink back down.

The scientists used a microscope camera and scattered green LED illumination to track the movements of the micromotors. The average speed of the devices increased when the NIR laser power increased. The team repeated the experiments with the micromotors placed in a water-based environment. The system showed convective motions too, but the propulsion through the air was much more efficient due to the reduction in viscous drag.

The researchers wrote in the paper that they envision a variety of applications for their micromotors, including gas-phase heterogeneous catalysis, aerosol toxin detection and pollution control. They also note that “given the light-driven, fuel-free nature of this system, future development could also explore solar-responsive micromotors for passive environmental remediation in open or semi-confined airspaces.”