Without further intervention, the rotation would go back and forth at random. Therefore, the team also dipped two electrodes into the solution and allowed an alternating current to flow. The alternating direction of tension altered the energy landscape experienced by the long DNA arms, making rotation in one direction more favorable through a mechanism known as the blinking Brownian ratchet.
This turned the passive devices into real motors. Micrographs show that under these conditions, each arm—although it shook randomly—always rotated in the same direction on average.
By itself, the nanomotor does nothing more than overcome the resistance of the surrounding solution. “It’s like swimming: you move forward and do a lot of work that evaporates in the water,” says Dietz. But to show that the motor could also do potentially useful work, the researchers went one step further: They attached another strand of DNA to their rotor and let it coil up like the hairspring used to turn the gears in a mechanical one clock is used. Such a mechanism could help nanomachines store energy or pull on other mechanical components, Dietz says.
For him, the motor is important first proof that the principle works and that not only static nanosystems can be produced with the help of DNA origami technology, but also ones that can do work. “Of course I was very happy about the publication of our work in ‘Nature’,” says Hendrik Dietz. “For me, it is above all an incentive to think directly about the next project.” After all, his chair has just been renamed from “Molecular Design” to “Molecular Robotics”.