Nanomotor rotates microscale objects

10 Mar 2006

In this week's Nature, researchers in the Netherlands unveil a nanomotor that can rotate objects 10,000 times its size.

Researchers in The Netherlands have created a nanomotor that can rotate microscale objects. The team, from the University of Groningen, Eindhoven University of Technology and Philips Research Laboratories, believe the development is an important step towards the use of molecular motors in nanomachinery. (Nature 440 163)

Rod on liquid crystal

"We demonstrate for the first time that a light-driven molecular motor can actually perform work by rotating a microscale object," said Ben Feringa of the University of Groningen. "The object is at least 10 000 times the size of each motor but to rotate it a collective action of several motor molecules is needed, which is reminiscent of the combined work of many protein motor molecules in our muscles."

Feringa and colleagues used a molecule with a central carbon-carbon double bond that functioned as an axle. The upper part of the molecule acted as a rotor while the lower part was the stator. The team added the molecules to a liquid crystal film and illuminated them with light with a wavelength of 365 nm.

The light caused a photochemical isomerization around the double bond and changed the helicity of the molecule from right- to left-handed. A thermal step then caused the molecule to revert to its right-handed state. Two sets of a photochemical step followed by a thermal step resulted in the molecule rotating through 360°.

"The change in shape of the propeller part of the motor during the rotary process causes a change in organization of the molecules of the liquid crystal material and a rotary change in the surface profile," said Feringa. "An object placed on top of the surface follows the change in surface profile, which leads to rotary motion. A comparison is a small boat floating on rotating waves."

The team used the motors to move glass rods with dimensions of 5 x 28 microns. The rod rotated at an average speed of 0.67 rpm during the photochemical steps and at 0.22 rpm during the thermal steps.

"The most important [result] is that we can induce motion and perform work," said Feringa. "This will not be directly useful as such, but a stepping stone to functional motors that can act as tiny machines or perhaps power a nanocar."