3D geometry of the four-wheeler on the copper surface in motion.
Credit: Randy Wind/Martin Roelfs
3D geometry of the four-wheeler on the copper surface with the wheel in rotation.
Credit: Randy Wind/Martin Roelf
LONDON: A single molecule has been used to create the world's smallest electric car. The 'four-wheel drive' car is just 1 nanometre in length and uses molecular motors to move across a metal surface.
Molecular motors are used throughout nature to build biological structures and enable bodily functions such as muscle contraction. For years scientists have been building their own synthetic versions of these motors with the ability to move molecules when forces are applied but have struggled to get them moving of on their own accord.
But now, publishing in the current issue of Nature, Ben Feringa's team at the University of Groningen in the Netherlands have developed the first single-molecule vehicle that can actively propel across a copper surface in a chosen direction. According to the researchers, they have taken "a decisive step on the road to artificial nano-scale transport systems".
First unidirectional car
The design consists of four rotary units attached to a single organic molecule, which change shape in response to incoming electrons and propel the molecule forward. The electrons are provided by way of a scanning tunnelling microscope that helps electrons jump into the molecule at the atomic level. The electrons act as a fuel to enable the shape changes needed for movement.
"The motors have two parts - a propeller which moves around an axis. The axle is a carbon-carbon double bond and when you excite it you temporarily break this double bond allowing a 360 rotary motion of the propeller function," explained Feringa.
"By controlling the clockwise or counter-clockwise rotation of the wheels, we could control the directionality of the movement. This is the first design where you really get molecular propulsion at the nanoscale and in a unidirectional sense."
The induced rotation allows the wheels to turn and the molecule to move forward across a linear trajectory, in this case a copper surface.
Building up from the fundamentals
Applications for these motors are far into the future as the main aim of this research is to understand these motors on the small-scale.
"If we can understand motion at these scales we can bring that to bigger systems," commented Paul Weiss, director of the California Nanoscience Insititute in the U.S.. "If we can learn to make these very small motors work together maybe we can follow some of the strategies nature has used in building up hierarchical structures. All our muscles for instance work by many motors working together."
Previous attempts to combine multiple motors have resulted in interference when operating. This design is the first time multiple motors have been seen to work in cooperation. "We're really just getting the first glimpses in this field," said Weiss. "This beautiful work by Feringa is exciting because four motors on one molecule are all working together to move something forward."
Molecular motors
Controlling movement on the nanoscale will however prove useful in the future development of molecular mechanical systems such as nano-robots used potentially to travel through the human bloodstream.
"To go to a device such as a nanorobot or nanomachine that may work in your blood veins or biological systems you need something to power it, you need motors. We are confident molecular motors will provide those motor functions in the future," said Feringa.
However the first challenge on this route is get the motors working in normal conditions as they are currently moving in temperatures of -266C.
"This is the first primitive step to get this propulsion. The next step will be to go to ambient conditions and see if we can move something along a trajectory as this is all in low temperatures and high vacuum," concluded Feringa. "But we have proved the principle, and once you prove a principle you can think about systems that are probably useful in the future".
