Light-driven synthetic nanorobots, comparable in size to a blood cell, could someday travel through the human body to aid surgeons in the removal of tumors and deliver targeted medications. A nanorobot that uses light as its propelling force has been demonstrated by a research team at Hong Kong University (HKU). The nanorobots, which were developed over a three-year period, have a novel nanotree structure, composed of two common, low-cost semiconductor materials: silicon and titanium oxide. To build the structure, the silicon and titanium oxide materials were shaped into nanowire and then further arranged into a miniaturized nanotree heterostructure. Professor Yinyao Tang showing the disc that contains millions of synthetic light-seeking nanorobots. Courtesy of the University of Hong Kong. The team developed an artificial microswimmer that could sense and orient to the illumination direction of an external light source. The microswimmer, a Janus nanotree, contains a nanostructured photocathode and photoanode at opposite ends that release cations and anions respectively, allowing it to be propelled by self-electrophoresis. Using chemical modifications, the team demonstrated control of the zeta potential of the photoanode and was able to program the microswimmer to exhibit either positive or negative phototaxis. The team’s nanorobot design was inspired by a species of green algae that has developed the ability to sense the intensity of light around it at a cellular level and then swim toward the light source so that photosynthesis can take place. In its experiments, the team was able to show that a school of its microswimmers could mimic the collective phototactic behavior of this green algae. Currently, the only method to remotely control nanorobots is to integrate a tiny magnet into the nanorobot and guide its motion through an external magnetic field. Given that nanorobots are only a few micrometers in size — about 50 times smaller than the diameter of a human hair — it can be very difficult to incorporate effective electronic sensors and circuits into them at a reasonable cost. Speaking about the light-driven nanorobots, professor Jinyao Tang said, "Although the current nanorobot cannot be used for disease treatment yet, we are working on the next generation nanorobotic system which is more efficient and biocompatible." "Light is a more effective option to communicate between the microscopic world and the macroscopic world,” said Tang. “We can conceive that more complicated instructions can be sent to nanorobots which provide scientists with a new tool to further develop more functions into a nanorobot and get us one step closer to daily life applications." The research was published in Nature Nanotechnology.