Robots smaller than a grain of salt? It sounds like science fiction, but researchers have developed autonomous microrobots that can move through liquids, sense their environment and operate independently using only light as a power source.

The microrobots, developed by researchers at the University of Pennsylvania and the University of Michigan, measure roughly 200 by 300 by 50 micrometers. Yet they can detect temperature changes, follow programmed paths and function independently for months at a time.

Their work was reported this week in two scientific journals, Science Robotics and Proceedings of the National Academy of Sciences.

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"We've made autonomous robots 10,000 times smaller," senior author Marc Miskin, assistant professor in electrical and systems engineering at Penn Engineering, said in a statement. "That opens up an entirely new scale for programmable robots."

Powered entirely by light, the robots don't move using mechanical limbs. Instead, they generate tiny electrical fields that push ions (electrically charged particles) in fluid to create motion, an approach better suited to the unique physics of the microscopic world, where traditional motors don't work.

Unlike earlier microrobots, these devices combine sensing, computing, decision-making and movement in a single, self-contained system at an extremely small scale.

Previous efforts in microrobotics have often relied on external controls, such as magnetic fields or physical tethers, to guide movement. These new microrobots, however, incorporate their own miniature solar cell-powered processors, allowing them to respond to their environment, communicate through patterned movements visible under a microscope and carry out tasks without outside direction.

Potential applications include monitoring biological processes at the cellular level, supporting medical diagnostics or helping assemble tiny devices. Because each robot can be mass-produced at very low cost, the technology opens new avenues for research and engineering at scales that were previously unreachable.