Source: Physics-World

A “four-wheel drive car” less than one billionth the length of an average SUV has been built and operated by researchers in the Netherlands and Switzerland. The molecular machine is about 1 nm long and uses electrons as fuel as it navigates across a copper surface. The tiny device could find use in nanometre-sized robotics or as tiny transporters that shift molecules around.

Molecular machines are common in nature. Motor proteins, for example, can move along a surface to transport molecular-sized cargo and are often used to build structures within living cells. Scientists would like to make their own versions of motor proteins, and indeed they have already designed and demonstrated single molecules that can move across surfaces. But these have been mostly passive: to ensure that they travel in a certain direction, they have had to be pulled or pushed.

Now, Ben Feringa of the University of Groningen and colleagues have demonstrated a truly active single-molecule vehicle. Constructed around an organic, carbon-based frame, it has four “wheels” or rotor parts, connected to the body via carbon–carbon double bonds. When the tip of a nearby scanning tunnelling microscope fires electrons at these bonds, they break and re-form the other way round. This process is known as isomerization and causes the wheels to turn, and the vehicle to move forward.

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