Light-Driven Nanorobots Learn to Hunt and Collect Bacteria

Researchers at Julius-Maximilians-Universitat Wurzburg (JMU) in Germany, led by professor Bert Hecht, have built microscopic robots that can search out, capture and relocate bacteria in water using nothing but light for power and steering. The machines, called microdrones, are about 50 times narrower than a human hair, and the newest versions are smaller than one micrometre, a millionth of a metre.

The robots move using photon recoil: nanoscale antennas on the device absorb light of a particular colour and polarization, then re-emit it in a specific direction. Because each redirected photon pushes back on the tiny, near-massless robot, that recoil is enough to propel and accelerate it, similar in principle to the recoil from firing a bullet. Changing the polarization of the incoming light rotates built-in antenna wires on the robot, letting researchers steer it, while the recoil keeps pushing it forward.

"In essence, we have built a light-driven nanorobot that can track down and collect bacteria," said Jin Qin, lead experimental scientist on the study. "By simplifying the design, we reached a size at which these robots can operate directly in the microbial world, almost like microscopic cleaning devices." The robots can make fast 90-degree turns to scan a sample efficiently, and can selectively capture, carry and release bacteria at chosen locations, effectively acting as microscopic cleaners under laboratory conditions.

"This is a striking example of how light can be used not only to observe the microscopic world, but also to actively shape it," said Hecht. "The idea of tiny robotic cleaners may sound futuristic, but we are already demonstrating the physical principles that make it possible." The robots stay maneuverable even while carrying a group of bacteria, though their speed drops under the added load, pointing to possible future uses in microbiology and biomedical research, the researchers found.