This car is on the cover of a magazine. You won’t be able to hear it when it’s running, because it doesn’t have sound. You won’t be to call it on its emissions, because it’s electric. And you sure won’t be able to see it with your naked eye because it’s 4×2 nanometers in size — you need a scanning tunneling microscope to see this sucker.
It’s the world’s smallest, four-wheel drive electric car and could very well never be unseated from that designation by anything smaller. Created by researchers at Empa and their Dutch colleagues, this nano-car runs happily along its copper paved road and is what the team calls “a decisive step on the road to artificial nano-scale transport systems.”
To carry out mechanical work, one usually turns to engines, which transform chemical, thermal or electrical energy into kinetic energy in order to, say, transport goods from A to B. Nature does the same thing; in cells, so-called motor proteins – such as kinesin and the muscle protein actin – carry out this task. Usually they glide along other proteins, similar to a train on rails, and in the process “burn” ATP (adenosine triphosphate), the chemical fuel, so to speak, of the living world.
They have synthesised a molecule from four rotating motor units, i.e. wheels, which can travel straight ahead in a controlled manner. “To do this, our car needs neither rails nor petrol; it runs on electricity. It must be the smallest electric car in the world – and it even comes with 4-wheel drive” comments Empa researcher Karl-Heinz Ernst.
The downside: the small car, which measures approximately 4×2 nanometres – about one billion times smaller than a VW Golf – needs to be refuelled with electricity after every half revolution of the wheels – via the tip of a scanning tunnelling microscope (STM). Furthermore, due to their molecular design, the wheels can only turn in one direction. “In other words: there’s no reverse gear”, says Ernst, who is also a professor at the University of Zurich, laconically.
After 10 simulations where electricity was applied to the car and observed with SMT, the car moved six nanometers forward in a relatively straight line:
Another experiment showed that the molecule really does behave as predicted. A part of the molecule can rotate freely around the central axis, a C-C single bond – the chassis of the car, so to speak. It can therefore “land” on the copper surface in two different orientations: in the right one, in which all four wheels turn in the same direction, and in the wrong one, in which the rear axle wheels turn forwards but the front ones turn backwards – upon excitation the car remains at a standstill. Ernst und Parschau were able to observe this, too, with the STM.
All-in-all this research shows that molecules can absorb external energy and move. The researcher’s now will see if the molecules can be driving by light, instead of electricity.