Researchers at Cornell University have developed the smallest walking robot yet, opening up new possibilities for advanced imaging and force measurements at the microscopic scale. These tiny robots, which are just 5 to 2 microns in size, can maneuver independently, interact with light waves, and perform intricate tasks such as moving across tissue samples to take images and measure forces at a scale previously impossible for conventional microscopes.

Led by Paul McEuen, the John A. Newman Professor of Physical Science Emeritus at Cornell’s College of Arts and Sciences, the team’s work represents a significant leap in both robotics and optical technology. The paper, Magnetically Programmed Diffractive Robotics, was recently published in Science, with McEuen as the corresponding author. Conrad Smart, a researcher at Cornell’s Laboratory of Atomic and Solid State Physics (LASSP), and Tanner Pearson, Ph.D. ’22, are co-first authors.

Cornell scientists had already set the record for the world’s smallest walking robot, measuring just 40–70 microns. However, these new robots are orders of magnitude smaller—ranging from 5 to 2 microns in size—and have the ability to perform tasks never before possible at such a tiny scale. “These robots are tiny, and we can control them precisely using magnetic fields,” said Itai Cohen, professor of physics and co-author of the study. “They are so small that they can interact with and shape light at a scale previously reserved for optics.”

What makes these robots particularly groundbreaking is their ability to work with light waves using a principle called diffraction, which occurs when light bends around objects or passes through narrow openings. For diffraction-based imaging to work effectively, the robots need to be on the same scale as the wavelength of visible light. This requirement—combined with the robots’ ability to move independently—has been the key challenge that the Cornell team has successfully overcome.

The robots are controlled using magnets that make them “pinch” forward, mimicking the motion of an inchworm. This motion allows them to walk on solid surfaces or “swim” through fluids, offering flexibility in a variety of environments. Their ability to move on their own and interact with light opens up exciting new possibilities for real-time imaging and force measurement at the microscopic level.

“The miniaturization of robotics has reached a point where these tiny systems can actively manipulate light at the scale of just a few wavelengths—about a million times smaller than a meter,” said Francesco Monticone, co-author of the study and associate professor of electrical and computer engineering. “This is a convergence of microrobotics and microoptics that allows us to do things that weren’t possible just a few years ago.”

To drive these robots at such a small scale, the researchers used a novel method involving nanometer-scale magnets embedded into the robots’ bodies. These magnets come in two distinct shapes: long and thin or short and stubby. The long magnets require a larger magnetic field to flip their orientation, while the shorter magnets need a smaller field. By applying different magnetic fields, the robots can be precisely controlled, enabling them to perform specific tasks like moving to desired locations or changing shape.

This approach, inspired by work at Fudan University by physicist Jizhai Cui, combined with thin film technology from the Cornell Nanoscale Science and Technology Facility, allowed the team to create robots with unprecedented movement and precision.

In addition to moving, these diffractive robots can measure forces by interacting with structures they encounter. Their flexible, spring-like nature allows them to compress when pressure is applied, which alters their diffraction pattern. By analyzing these changes, researchers can measure the forces exerted on the robots with remarkable accuracy.

The combination of force measurement and optical abilities positions these robots as valuable tools for both basic research and potential clinical applications. For instance, the robots could be used to explore DNA structure or perform high-resolution imaging at the cellular level.

“I’m excited by the potential of these robots to perform super-resolution microscopy and other sensing tasks while moving across the surface of a sample,” said Monticone. “We are just beginning to scratch the surface of what is possible with this new fusion of robotics and optics at the microscale.”

Looking ahead, the researchers envision swarms of these diffractive microbots working together to perform complex imaging tasks, such as super-resolution microscopy, or monitoring biological structures in real-time. Their ability to move independently, manipulate light, and measure forces opens up a world of possibilities, from medical diagnostics to advanced scientific research.

“We believe this new approach to microrobotics and optical engineering could revolutionize a wide range of fields, from biomedicine to materials science,” McEuen concluded. “This is a truly exciting step forward, and we can’t wait to see where this technology will go next.”

With these miniature robots, Cornell has once again pushed the boundaries of what is possible in the world of microengineering, offering a glimpse into the future of scientific discovery and healthcare technology.

By Impact Lab