Photon-powered nanomotor transforms light directly into motion

Most solar powered motors require an intermediate step where the light is converted to electricity or heat, usually by a photovoltaic cell, before it can be used to drive the motor. But now a team of University of Florida chemists have developed a new type of “molecular nanomotor” that bypasses this step and transforms light directly into motion – albeit on a very tiny scale.

While this is not the first small-scale motor driven directly by light we've encountered, it is the first built entirely with a single molecule of DNA. This gives it a simplicity that increases its potential for development, manufacture and real-world applications in areas ranging from medicine to manufacturing. It also makes it biocompatible, meaning it could become a component of microscopic devices that repair individual cells or fight viruses or bacteria inside the human body. The team say it also produces no waste, is easy to assemble, has fewer parts and theoretically should be more efficient than other solar powered motors.

The nanomotor is almost vanishingly small, measuring just 2 to 5 nanometers (or 2-5 millionth of a millimeter) in its clasped form and extending to as long as 10 to 12 nanometers in its unclasped form. Although scientists say their calculations show it uses considerably more of the energy in light than traditional solar cells, the amount of force it exerts is proportional to its small size.

The incredibly small scale means that larger applications such as powering a vehicle, running an assembly line or otherwise replacing traditional electricity or fossil fuels would require untold trillions of nanomotors, all working together in tandem. While this poses a challenge, the team is working on a way to collect the molecular level force into a coherent accumulated force that can do real work when the motor absorbs sunlight.

To make the nanomotor, the researchers combined a DNA molecule they created in the lab with azobenzene, a chemical compound that responds to light. A high-energy photon prompts one response and a lower energy one another. To demonstrate the movement, a fluorophore, or light-emitter, was attached to one end of the nanomotor and a quencher, which can quench the emitting light, to the other end. Their instruments recorded emitted light intensity that corresponded to the motor movement.

The University of Florida team is expected to publish their findings in the online edition of the journal Nano Letters.