Researchers at Cornell University have built the world’s smallest walking robot, at just two to five microns across. The robot is so small that over 3o,ooo of them could fit on the sharp point of a needle. That tiny size means potentially huge capabilities for medical uses and material sciences since it is small enough to interact with waves of light at sizes comparable with the light’s wavelength.
“A walking robot that’s small enough to interact with and shape light effectively takes a microscope’s lens and puts it directly into the microworld,” says team leader Paul McEuen, an emeritus professor of physical science at Cornell. “It can perform up-close imaging in ways that a regular microscope never could.”
Cornell says this is the first implementation of diffractive robotics: untethered robots that have imaging capabilities at extreme micro-scale. These imaging techniques rely on visible light diffraction, which is the bending of a wave of light when it passes through an opening.
To put this in context, the robots are up to five microns across. That’s 5,000 nanometers, because a micron is one-millionth of a meter while a nanometer is one-billionth of a meter. Another way to think about it: if a nanometer were the size of a marble, a micron would be the size of a basketball. Since wavelengths of light in the visible spectrum range from 400-700 nanometers, you can see how a robot this small could include structures used for imaging at the nano-scale.
“The miniaturization of robotics has finally reached a point where these actuating mechanical systems can interact with and actively shape light at the scale of just a few wavelengths—a million times smaller than a meter,” says co-author Francesco Monticone, an associate professor at Cornell.
The robots have to be that small to make the optics work. But they also have to be mobile to get to the targets that researchers want to image. Cornell says this team has achieved both objectives.
Of course, the robots don’t exactly “walk” the way you or I do, or the way a large-scale humaniform factory robot does. And they don’t exactly carry an extremely tiny on-power battery or power supply.
Instead, they’re controlled via magnetic fields.
Each tiny, invisible micron-scale robot is patterned with hundreds of even tinier nano-scale magnets, some long and thin, and some short and stubby, Cornell says. And that enables movement via manipulation of magnetic fields.
“The long, thin ones need a larger magnetic field to flip them from pointing one way to pointing the other, while the short, stubby ones need a smaller field,” study co-author Itai Cohen, a professor of physics, said. “That means you can apply a big magnetic field to get them all aligned, but if you apply a smaller magnetic field, you only flip the short, stubby ones.”
The result is a short of inch-worm wriggle, or “walking.” The robots can also “swim” through a fluid to achieve the same result, Cornell says.
To actually image, the robots can mechanically move their diffractive elements. They can be used in conjunction with larger microscope lenses, or, theoretically, on their own.
Visible light diffraction imaging techniques are already used for multiple scientific and industrial purposes, including optical microscopy to study cells and tissues, interferometry to detect tiny surface irregularities in lenses and mirrors, and super-resolution microscopy to examine proteins or cellular processes.
Future uses with micro-scale robots could include medical applications.
“Looking to the future, I can imagine swarms of diffractive microbots performing super-resolution microscopy and other sensing tasks while walking across the surface of a sample,” Francesco Monticone said in a statement. “I think we are really just scratching the surface of what is possible with this new paradigm marrying robotic and optical engineering at the microscale.”
