Wow! World’s tiniest car made of a single molecule takes its first spin. This absolutely minute car has four wheel-like paddles that spin in the same direction when activated with a beam of electrons.

Syuzanna Harutyunyan, a chemist at the University of Groningen in the Netherlands participated in designing world’s tinniest car, says;

“The molecule is autonomous; you don’t need to touch it. Just give it energy and it’s capable of converting that energy into movement.”

The nanocar is quite able to ship tiny loads of cargo and to untie why miniature motors in nature tend to be so much more efficient than large-scale ones.

To create the nanocar, Harutyunyan and her team designed a molecule with a long central body and one pivoted paddle at each of four corners. The paddles are free to swing around in circles, not unlike wheels.

Ordinarily they arrange themselves so as to minimise crowding with the central body, as this costs the molecule the least amount of energy. But when the team applies a pulse of electrons to the “wheels”, some gain energy and move a quarter turn.

Frigid temperatures of 7 kelvin (-266 °C) help this clunky forward motion by effectively freezing the wheels in place except when excited by the electron pulse and during their subsequent self-adjustment. This keeps them from rolling backwards.

Nanocar takes a test drive

It's the smallest thing on four wheels

Philip Ball

Vroom: this nanocar is made from a single molecule.© Y. Shira/Rice University

The world's smallest toy cars have been set rolling.

They measure just 3 by 4 nanometres: a million of them parked bumper to tail would cover the length of a flea. And they are stripped down to the absolute basics: just a chassis and two axles with wheels at either end.

But they move. Using a powerful microscope, James Tour and his coworkers at Rice University in Houston, Texas, have watched their 'nanocars' trundle over a layer of gold¹.

The axles and chassis are made primarily of carbon atoms linked into rigid rods that form an H shape. At each axle tip, the researchers attached a ball-like wheel made from the football-shaped carbon molecule C₆₀.

The key question was whether these diminutive vehicles truly roll over a surface, or just skitter about because of their thermal energy, as many molecules do.

Wheel spin

Tour and his colleagues claim that the wheels must indeed be turning. When they used the fine tip of a scanning tunnelling microscope, a device normally used for imaging at the atomic scale, to attract the nanocars and pull them along, the cars moved forward but not sideways. That's just what you would expect to happen if the C60 molecules were rotating on an axis. Occasionally the cars pivoted and took off in a new direction, making zigzag paths.

Three-wheeled nanocars with tripod axles could only turn in circles, again as would be expected if the wheels were revolving.

"This is really exciting", says materials scientist Henry Hess of the University of Florida in Gainesville, who has used biological molecular motors to drive nanoscale objects over surfaces.