A report published last month created a very simple partially biological robot closing in on nanobot size. Researchers grew bacterial spores only 2000-5000 nanometers (nm) across, sprinkled with even smaller specks of material only 150 nm wide. Researchers call these specks graphene quantum dots, a fancy way of describing really small flakes of graphite, one atom thick.
The study harnesses the spore’s naturally evolved ability to detect and respond to ambient humidity. The bacteria spore will swell in the presence of more external water and shrivel if conditions dry out. Meanwhile the graphite flakes spread across its outer skin are stuck in place. If the skin underneath swells like a balloon, the flakes riding upon it will spread further apart.
The tiny robotic spores are then sent to crawl across tiny electrodes drawn onto a surface. A voltage is applied to each pair of electrodes, making electrons want to travel from one electrode to the other. If air separates the electrodes, no electricity will flow. If a spore is crawling across the electrodes, some electrical current will hop across its body, from one graphite fleck to the next, bridging the gap.