That capability could be especially useful for biological materials in water, including individual cells and bacteria. Precisely controlling and moving objects at this scale has been a persistent challenge. The newly developed nanorobots show that it is already possible to collect bacteria, transport them, and release them at selected locations.

Light Powers and Steers the Tiny Robots

One of the biggest obstacles in developing machines this small is finding an effective way to propel and control them. At Julius-Maximilians-Universität Würzburg (JMU), a research team led by Professor Bert Hecht has been developing a solution that uses the recoil produced by individual photons to move microscopic devices known as microdrones.

The devices contain as many as four plasmonic nanoantennas. These antennas absorb light with a particular color and helicity, then emit that light in a specific direction. Redirecting each photon creates a tiny recoil force, similar in principle to the recoil produced when a bullet is fired. Because the microdrones have so little mass, those extremely small forces can generate substantial acceleration and speed.

For the latest work, the researchers reduced the size of their light-powered robots even further, producing devices smaller than one micrometer. Simplifying the steering system was an important part of achieving that size while retaining propulsion based on photon recoil.

The new control method takes advantage of nanoscale antenna wires built into the robot. These wires naturally tend to align with the polarization direction of incoming light. By changing the light's polarization, the researchers can control which direction the nanorobot faces. At the same time, photon recoil continues to propel it forward, creating a steering system that works somewhat like the directional control used in larger vehicles.

Nanorobots Act as "Microscopic Cleaners"

"In essence, we have built a light-driven nanorobot that can track down and collect bacteria," says Jin Qin, lead experimental scientist of 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 are also highly maneuverable. They can make extremely fast 90° turns, helping them scan broad areas of a sample in an organized and efficient way. They can also selectively capture, carry, and release substantial numbers of bacteria.

Under controlled laboratory conditions, this means the nanorobots can effectively "clean" microscopic environments. They gather bacteria from one area and deposit them at specifically chosen locations.

"This is a striking example of how light can be used not only to observe the microscopic world, but also to actively shape it," adds Bert Hecht. "The idea of tiny robotic cleaners may sound futuristic, but we are already demonstrating the physical principles that make it possible."

The robots remain fully maneuverable even while carrying larger groups of bacteria, although their speed decreases somewhat under the added load. That ability to keep functioning while transporting larger bacterial clusters points to possible future uses in microbiology, biomedical research, and precise manipulation of materials at the microscopic scale.