Submarines are going microscopic. Tiny tubes about 10 micrometres long can propel themselves using only sunlight and can be steered by magnetic fields. These microrobots could be useful for cleaning up toxic waste.
Most swimming microrobots can only move in two dimensions: depending on their weight, they either sink to the bottom of a liquid or float close to the surface as they swim around. at the University of Chemistry and Technology in the Czech Republic and his colleagues built a microrobot that can be steered in any direction, including up or down, and requires only sunlight to power it.
鈥淚n normal robotics, you have wheels and circuits and so on, but on such small scales we cannot really do it, so we mimic nature rather than mimicking larger robots. We make them work as microorganisms do,鈥� says Pumera. 鈥淭hey move themselves and they take energy from the environment as living organisms do.鈥�
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The tubular microrobots, which Pumera and his team have dubbed microsubmarines, are built with three main layers. On the inside of the tube is a layer of cadmium sulphide, which takes in light and releases electrons. Those then react with water to split it into its constituent parts and generate a small amount of thrust. This pushes the tube forward at speeds up to about 15 micrometres per second.
The middle layer is made of iron nanoparticles, which make it possible to steer the microsubmarine using magnetic fields. Finally, comes an outer layer of titanium dioxide. When exposed to light, this layer catalyses reactions that degrade many chemicals, allowing the microsubmarine to clean up polluted water.
The microrobots were tested in water polluted with picric acid, which is an explosive, and a type of dye that can be harmful to the environment. Over 2 hours, they broke down more than 70 per cent of the pollutants, although in practice you would probably need large quantities of microsubmarines to clean up any significant pollution, says Pumera. These could then be retrieved with a magnet.
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