Tiniest car gets a test drive

Zap of electricity propels nano-motors

ON A ROLL  A mini four-wheeled vehicle rolls across a surface when zapped with electricity that contorts the wheels’ axle. 

Randy Wind/Martin Roelfs; Nature

Scientists have created the tiniest electric car ever — although it won’t be coming to your local dealership anytime soon. With four molecular wheels and a carbon-based frame, the mini-roadster is a step toward devices that mimic the machinery of molecular life.

The researchers started with little motorized “wheels,” molecules inspired by the motors that some bacteria use to propel themselves, and attached them to a frame. A carbon double bond serves as an axle between two wheels; when the entire unit is zapped with electricity, the double bond becomes a single bond. This contorts the axle, rotating the wheels and propelling the car forward, researchers report in the Nov. 10 Nature. In test drives on a copper surface the car went as far as 20 nanometers, says organic chemist Ben Feringa — about 10 car lengths.

Designing a contraption that will do your bidding in the nanoworld is not so easy, says Feringa, of the University of Groningen in the Netherlands. With regular-sized cars, forces such as gravity dictate interactions with the road. But a vehicle that’s nanometers long — about the width of a DNA molecule — must contend with different forces.

“The interactions with the surface are very important,” Feringa says. “The key is to not make it stick to the surface, because it will never move, but also it cannot fly away.”

Another difficulty of working at the nanoscale is when molecules are close together they interact, and not necessarily in the way that you want, says Paul Weiss, director of the California NanoSystems Institute at UCLA.

“The biggest thing here is these four motors operating together,” says Weiss, who wrote a commentary accompanying the Nature article.  “It’s really terrific work.” 

Nature is adept at making such minimachines. There are proteins that transport cargo inside cells, others that help muscles move and pumps that provide energy. Building similar molecules that cooperate and carry out tasks could lead to all sorts of machines and uses, Weiss says.

There are still kinks to iron out before these little cars can be mass-produced efficiently. The molecular machines are made in a solution that’s then poured on the copper surface, and only cars that land right-side-up are drivable. But such production issues should be relatively easy to overcome, says Weiss.

“We’re really learning the forces and the lay of the land at the nanoscale,” he says.

The researchers would like to see whether they can propel the machines with light rather than electricity, says Feringa, and also plan to add cargo to see whether the vehicles can carry a load.

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