World’s smallest programmable robots think, swim, and sense temperature using light

Robots have just shrunk to the size of microorganisms.

Researchers at the University of Pennsylvania have unveiled what they describe as the world’s smallest fully programmable, autonomous robots, sporting a brain developed at the University of Michigan.

These microscopic swimming machines can sense their surroundings, make decisions, and operate independently for months at a time.

Barely visible to the naked eye, each robot measures about 0.2 by 0.3 by 0.05 millimeters, placing it squarely at the scale of bacteria and single-celled organisms.

Despite their size, the robots can move in complex patterns, respond to temperature changes, and even coordinate their motion in groups.

What makes them especially striking is their cost and longevity.

Each robot costs roughly a penny to make, runs on light, and contains no moving parts, a design choice that makes it remarkably durable despite operating in fluid environments.

Together, the machines represent a long-awaited breakthrough in microscale robotics, a field that has struggled for decades to combine independent motion, sensing, and computing at extremely small sizes.

Robots at microbial scale

For years, electronics have steadily shrunk, but robots have lagged behind. Independent motion at the microscale has been particularly challenging, largely because water behaves very differently at tiny scales.

“We’ve made autonomous robots 10,000 times smaller,” said Marc Miskin, assistant professor in electrical and systems engineering at Penn and senior author of the research.

“That opens up an entirely new scale for programmable robots.”

Operating in water at this scale is less like swimming and more like pushing through thick syrup.

Instead of propellers or joints, the robots use an elegant workaround: they move the surrounding fluid itself.

Rather than pushing against water directly, the robots generate an electric field that nudges ions in the liquid.

Those ions then push on nearby water molecules, creating thrust that moves the robot forward.

This propulsion system has no moving parts, allowing the robots to swim for months and be transferred easily using a micropipette.

They can also travel in coordinated groups, moving together much like schools of fish.

A brain powered by light

The robots’ intelligence comes from ultra-miniaturized computers developed at the University of Michigan.

These tiny processors must run on just 75 nanowatts of power, about 100,000 times less than a smartwatch.

“We saw that Penn Engineering’s propulsion system and our tiny computers were just made for each other,” said David Blaauw, a senior author of the study.

To make this possible, the team had to radically redesign how programs are written and executed at the microscale.

“We had to totally rethink the computer program instructions, condensing what conventionally would require many instructions for propulsion control into a single, special instruction,” Blaauw said.

Most of each robot’s surface is covered by solar cells, which harvest light for power and also double as optical receivers.

Light pulses are used both to power the robots and to program them, with each robot carrying a unique identifier that allows it to receive individualized instructions.

The current generation is equipped with temperature sensors capable of detecting differences within a third of a degree Celsius.

The robots can move toward warmer areas or report temperature changes by wiggling, a behavior likened to the honeybee “waggle dance.”

“This is really just the first chapter,” Miskin said. “We’ve shown that you can put a brain, a sensor and a motor into something almost too small to see, and have it survive and work for months.”

Future versions could carry additional sensors, store more complex programs, or operate in harsher environments, potentially transforming medicine and microscale manufacturing, according to the journal Science Robotics.