Nanorockets powered by a benign rocket fuel, which could one day carry drugs around the body have been built by German scientists.
Nanotubes filled with rocket fuel act like missiles, propelling themselves through liquids at eye-watering speeds.
But fuels such as hydrazine are toxic so can't be used inside the body.
Now, Samuel Sanchez and colleagues at the Leibniz Institute for Solid State and Materials Research in Dresden, Germany, have made the tiny rockets work with a less toxic fuel, New Scientist reported.
They designed nanotubes by rolling platinum-coated sheets of metal into tubes with the platinum on the inside.
When the team placed the tubes in a warm, weak solution of hydrogen peroxide, the platinum catalysed the decomposition of peroxide into water and oxygen.
This forced bubbles of gas out of one end of the tube, generating thrust in the opposite direction.
The result is a nanorocket that travels up to 200 times its own length per second, faster than the quickest bacteria.
The team can steer the tubes using a magnetic field and control the speed by varying the temperature of the fluid.
The fuel is only 0.25 per cent peroxide, but even this isn't entirely safe.
So, they are working to develop rockets that work with even less peroxide or a substance that is already present in the body, such as glucose.
The study was published in the Journal of the American Chemical Society.