Cornell researchers have developed the smallest walking robots ever created.

These tiny machines, measuring just 2 to 5 microns—thinner than a strand of hair—are designed to interact with light and move independently.

Their purpose?

To navigate microscopic environments, such as tissue samples, and capture images or measure forces in places traditional tools cannot reach.

“A walking robot this small essentially takes the lens of a microscope and puts it directly into the microworld,” explained Paul McEuen, a professor emeritus of physics and leader of the study. “It can provide up-close imaging that traditional microscopes simply can’t achieve.”

The study, published in Science, introduces “diffractive robotics,” which combines the tiny robots’ ability to move with advanced imaging techniques using light.

This breakthrough allows the robots to interact with light waves to produce highly detailed images. It also enables them to maneuver precisely on solid surfaces or “swim” through fluids, powered by magnetic fields.

The robots’ movements are controlled by magnetic patterns on their surface. By using different shapes of magnets, the researchers can control the robots’ motion with great precision.

For example, a larger magnetic field moves all the robots, while smaller fields can target specific ones. These innovations came from a collaboration of experts at Cornell, led by Itai Cohen, a professor of physics, and Francesco Monticone, an expert in optical engineering.

“This combination of microrobotics and microoptics is truly exciting,” Monticone said. “We’ve reached a point where tiny robots can not only move but also actively shape and interact with light, opening up incredible possibilities.”

The robots’ ability to interact with light comes from special “diffractive elements” built into their structure.

These elements allow the robots to manipulate light for tasks like focusing, tuning, or capturing super-detailed images.

The robots can also act as tiny extensions of a microscope, bringing the lens closer to the sample for improved imaging.

In addition to capturing images, the robots can measure forces at the microscopic level. By using their magnetic-driven pinching motion, the robots can detect how much pressure a structure exerts on them, making them useful for studying forces in DNA or other biological systems.

Looking ahead, the researchers envision swarms of these robots working together to perform tasks like high-resolution imaging or sensing in medical or research settings.

“This is just the beginning of what’s possible with these tiny robots,” Monticone said. “We’re excited to explore the many ways they can advance science and technology.”

This work was supported by the National Science Foundation, the Cornell Center for Materials Research, and the Cornell NanoScale Science and Technology Facility.