Cornell University researchers from the fields of physics and engineering have achieved a remarkable feat: the creation of the world’s smallest walking robot. This groundbreaking innovation is designed to interact with visible light waves while being diminutive enough to navigate and capture images within biological structures, such as tissue samples.

According to Paul McEuen, the John A. Newman Professor of Physical Science Emeritus, who led the research team, “A walking robot that interacts with and shapes light effectively positions a microscope’s lens right into the microworld. It enables unprecedented close-up imaging possibilities that traditional microscopes simply cannot achieve.”

The team’s paper, titled “Magnetically Programmed Diffractive Robotics,” has been published in the esteemed journal Science, with McEuen as the corresponding author. Other contributors to this significant research include Conrad Smart, a researcher at Cornell’s Laboratory of Atomic and Solid State Physics (LASSP), and Tanner Pearson, Ph.D. ’22, who served as co-first authors.

Prior to this development, Cornell scientists already held the record for the smallest walking robot at 40–70 microns. However, the new diffractive robots are set to far surpass this benchmark.

Itai Cohen, a professor of physics and co-author of the study, expressed excitement about the new robots, stating, “These robots measure between 5 microns to 2 microns in size. They’re incredibly small, and we can control their movements utilizing magnetic fields.” This innovative technology allows for precise navigation and interaction with minute entities.

This new approach to robotics connects untethered robots with imaging techniques reliant on visible light diffraction — the bending of light waves as they pass through an opening or around obstacles. This phenomenon requires openings comparable in size to the wavelength of light, making the scale of the new robots essential for successful operation.

The Cornell team has achieved both the ability for movement and the requisite size for the optics to function effectively. These robots are actuated by magnets that create a pinching motion, enabling them to inchworm forward on solid surfaces and swim through fluids.

The integration of maneuverability, flexibility, and optical capabilities represents a significant leap in robotics technology, promising breakthroughs in various scientific fields.

Francesco Monticone, an associate professor of electrical and computer engineering at Cornell, expressed his enthusiasm: “This convergence of microrobotics and microoptics is exhilarating. The miniaturization of robotics has reached a point where these systems can interact with and actively manipulate light on a scale one million times smaller than a meter.”

The driving mechanism behind these miniature robots utilizes patterned nanometer-scale magnets, which come in two distinct shapes: long and thin, or short and stubby. According to Cohen, this ingenious design, originally conceived by physicist Jizhai Cui from Fudan University, allows the robots to be controlled with precision under varying magnetic fields.

Cornell scientists have merged this innovative principle with ultra-thin films created at the Cornell Nanoscale Science and Technology Facility to develop the new robots effectively.

One of the main challenges faced in this optical engineering process was identifying the ideal approach for three key tasks: tuning light, focusing, and achieving super-resolution imaging. Different methods entail various performance trade-offs, influenced by the robots’ movement capabilities.

Mechanical mobility of the diffracting elements enhances imaging quality by allowing the robot to act as both a diffraction grating and a diffractive lens, serving as an extension of the microscope lens that observes the sample from above.

The robots possess the ability to measure forces by utilizing their magnetic pinching motion to exert pressure against target structures. As Cohen elaborated, “These robots behave like compliant springs — squeezing as they encounter pressure, which alters the diffraction pattern, allowing us to obtain precise measurements.”

The combined force-measuring and optical functionalities hold immense promise for both fundamental research, such as DNA structure analysis, and potential clinical applications.

Looking forward, Monticone envisions a future where swarms of these diffractive microbots conduct super-resolution microscopy and sensory tasks while traversing sample surfaces. “We are merely scratching the surface of potential innovations joining robotics and optical engineering at the microscale,” he concluded.