22 Sep 2025
Optical metamaterials offer route to “smallest on-chip motors in history.”
Small-scale geared mechanisms driven by the action of incident light could have a significant impact in multiple fields, including the design of micromachines and novel force sensors.
Recent studies into the practical applications of such tiny motors have seen them used to control localized release of drugs within the intestines of patients, and exploited their ability to produce both motion and fluorescence from the same motor component.
A project at the University of Gothenburg has now leveraged the behavior of optical metasurfaces to fabricate geared mechanisms on a micron scale, paving the way for “the smallest on-chip motors in history.”
Described in Nature Communications, the findings should unlock new possibilities for micro- and nanoscale systems, according to the Gothenburg team.
“Various mechanisms have been explored to power individual micromotors, however incorporating these micromotors into functional microscopic geared mechanisms remains a significant challenge,” noted the project in its paper. “Light-based methods are less constrained by material properties but require focused light beams, limiting their large-scale manipulation potential. A scalable approach for microscopic geared mechanisms that overcomes all limitations remains elusive.”
The Gothenburg solution employed optical metamaterials to create mechanisms that operate under uniform illumination, offering a more versatile platform for precise control and movement of functional devices in micro- and nanoscale mechanical systems.
“This is a fundamentally new way of thinking about mechanics on a microscale,” commented Gan Wang from Gothenburg’s Soft Matter Lab.
Manipulation of bacteria and cells
The mechanism’s metasurface was patterned with unit cells composed of two asymmetric silicon blocks separated by a subwavelength gap of 50 nanometers, designed to interact with 1064-nanometer plane illumination. This sits above a supporting silicon dioxide ring, anchored by a capped pillar that allows the metarotor to rotate freely.
Incident light shining on the metamaterial makes the gear wheel spin, with the intensity of the laser light controlling the speed of rotation. Changing the polarization of the illumination can change the direction of the gear wheel.
“We have built a gear train in which a light-driven gear sets the entire chain in motion,” said Gan Wang. “The gears can also convert rotation into linear motion, perform periodic movements and control microscopic mirrors to deflect light.”
One area set to benefit from this kind of improved micromotor could be biooptics and medicine, including the manipulation of bacteria and cells. A 1064-nanometer laser minimizes potential damage to biological samples, and if the light can be selectively directed to the driving gear then passive structures can be mechanically actuated with directly exposing biological material to the light source.
Since a gear wheel can be as small as 16 to 20 microns and there are human cells of that size, Gan Wang believes medical applications are within reach.
“We can use the new micromotors as pumps inside the human body, for example to regulate various flows,” said Wang. “I am also looking at how they function as valves that open and close. By replacing bulky couplings with light, we can finally overcome the size barrier.”