Researchers at Rice University have created a single molecule submarine that can be propelled by hitting the molecule with a beam of light. The research is reported in a (highly technical) paper on NanoLetters.
The molecule is made by 244 atoms, part of them able to rotate when hit by ultraviolet light. Each rotation moves the molecule forward by 18 nm. This does not seem like a big deal but each rotation takes a µs which means that in one second the molecule can travel close to one inch, and that is quite a long distance and an amazing speed for a molecule. According to the researchers it is the fastest moving molecule in a fluid that has ever been designed.
It is not the first time that nanomotors have been designed, the same research team has designed some time ago a nano-car with its four wheels that can propel it, but so far the propulsion required some substance that was either toxic or generated toxic waste. This is the first time that propulsion is achieved through light.
The motor itself looks, and works, like the flagellum of a bacteria. It bends and oscillates.
Of course the goal is to have these submarines to carry some payload, like another molecule that serves as a drug with the submarine acting as the vector. Notice that the progress needed is not trivial. First the submarine today moves forward but it cannot steer and as a single molecule negotiating its way among billions of other molecules it is continually subject to bumping and random pushes changing its direction. Secondly, having another molecule to piggy back on a single, relatively small molecules is really tricky!