A research team from Julius Maximilian University of Würzburg in Germany, led by Professor Bert Hecht and researcher Jin Chen, has succeeded in developing microscopic light-powered robots capable of hunting down, collecting, and transporting bacteria with pinpoint accuracy, in what resembles the “microscopic cleaning crews” of the future.
These nanorobots are less than one micrometer in size, meaning they are about 50 times smaller than the diameter of a human hair, allowing them to operate and move directly within liquid microbial environments.
Physics of photons
The idea of pushing and guiding these robots is based on the physics of photon bounce, as they are equipped with plasmonic nano-antennas that absorb light and re-emit it in specific directions.
This process generates a precise recoil force similar to the recoil of a weapon when a bullet is fired, and given the extremely small mass of robots, this force is sufficient to propel them at remarkable speeds and accelerations.
The researchers also devised a guidance mechanism based on nanowires inside the robot that automatically align with the polarization direction of the light, enabling scientists to control the robot's path and rotate it at sharp angles of up to 90 degrees simply by changing the polarization of the light.
The process of trapping the bacteria was not purely mechanical, but rather relied on utilizing subtle physical forces known as "thermo-optical kinetic forces," whereby when light is shone on the robot, it creates an infinitesimal thermal gradient that attracts surrounding microorganisms and keeps them confined within its field as it moves.
The team has thus overcome one of the biggest historical obstacles in nanoscience, which is the difficulty of grasping soft biological bodies without damaging them or affecting their vital functions, allowing the transfer of entire populations of microbes at once without the need for physical tweezers or complex chemical adhesives.
Laboratory experiments published in a study in the journal Nature Communications demonstrated the ability of these robots to effectively scan aquatic samples, capture clusters of bacteria, transport and discharge them at specific locations, while maintaining their maneuverability even while carrying large numbers of microbes.
According to the study, this innovation represents practical proof that light can be used not only to observe the microscopic world but also to actively control and shape it.
This opens up promising prospects and broad future applications in the fields of microbiology, biomedicine, drug targeting, and precise cleaning of contaminated samples at the cellular level.
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