Science fiction often envisions the future as a playground of hulking robots, enormous intelligent computer networks, and miles-long spaceships. Storytellers even describe building spherical shells millions of miles across. Vast irresistibly powerful machines rule the world of tomorrow.

Nanobots build the same future in precisely the opposite way. The world is peacefully administrated--or terrorized--by robots as small as a single virus. Uncountably vast swarms of these minute robots drift through the air like dust or gang together to build larger structures atom by atom.

Scientists and engineers watching the progress of microscopic technology were the first to imagine manufacturing large matter atom by atom from scratch using nanometers-long machines. Upon the command to build, a massive number of these machines would grab every single atom needed for the project and put them together, one by one. Are these nanobots far-fetched? Yes. Technology like this would likely take centuries to develop if it is feasible at all.

Still, scientific progress continues to realize smaller and smaller machines. A report published last month created a very simple partially biological robot closing in on nanobot size. The paper can be read in its entirity for free. 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 biological underpinning of these devices is very necessary. The machinery of DNA evolved over eons to create natural autonomous organisms capable of performing the remarkably complex tasks of building cells, changing those cells in reaction to external conditions, finding, capturing and digesting food, and replicating. All of this fits in a capsule a few thousand nanometers across. Nothing scientists have engineered comes even close to packing this level of capability into such a small volume.

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. However, 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. The drier the air, the closer together the flakes scrunch, the more electricity can bridge its way across the spore and into the opposite electrode. Researchers measure the rate of current flow and look for changes indicating varying humidity.

This discovery is one of many works taking the first tiny steps toward building nanobots, or at least slightly bigger microbots. The true limits of how small we can make things is unclear. As pointed out in an insightful (but pay-walled) commentary article in the journal Nature, the only nanobots that are currently feasible are those which use the incredibly powerful and tiny mechanisms of DNA-based biology to achieve their task of manipulating individual molecules. Nothing we design with our own hands is yet remotely close to this level of capability. Some of my own research requires a 100-pound instrument to manipulate a single molecule, and an attached modern computer to try it with any autonomy. Manipulation fails 99% of the time.

So, we have no reason to fear our robot overlords yet. We continually improve our abilities to manipulate the small, but the goal of creating a multitude of nanorobots with the power to build matter from the ground up, atom by atom, molecule by molecule, remains science fantasy.

(Image: AP)