Molecular-sized motor created from DNA

The tiny machine made of genetic material self-assembles and converts electrical energy into kinetic energy. The nanomotors can be switched on and off and the rotation speed and rotational direction can also be controlled.

The researchers used what is known as the DNA “origami method” to construct the nanoscale molecular rotary motor. Several long single strands of DNA serve as a basis to which additional DNA strands attach themselves as counterparts. The DNA sequences are selected in such a way that the attached strands and folds create the desired structures.

“We’ve been advancing this method of fabrication for many years and can now develop very precise and complex objects, such as molecular switches or hollow bodies that can trap viruses. If you put the DNA strands with the right sequences in solution, the objects self-assemble,” said TUM professor Hendrik Dietz.

The new nanomotor made of DNA material consists of three components: base, platform and rotor arm. The base is approximately 40 nanometres high and is fixed to a glass plate in solution via chemical bonds on a glass plate.

A rotor arm of up to 500 nanometres in length is mounted on the base so that it can rotate and a platform that lies between the base and the rotor arm is also attached. This platform contains obstacles that influence the movement of the rotor arm. To pass the obstacles and rotate, the rotor arm must bend upward a little.

Without energy supply, the rotor arms of the motors move randomly in one direction or the other, driven by random collisions with molecules from the surrounding solvent. However, as soon as AC voltage is applied via two electrodes, the rotor arms rotate in a targeted and continuous manner in one direction.

“The new motor has unprecedented mechanical capabilities. It can achieve torques in the range of 10 piconewton times nanometer. And it can generate more energy per second than what’s released when two ATP molecules are split,” said Ramin Golestanian, who led the theoretical analysis of the mechanism of the motor.

The targeted movement of the motors results from a superposition of the fluctuating electrical forces with the forces experienced by the rotor arm due to the ratchet obstacles.

The researchers can control the speed and direction of the rotation via the direction of the electric field and also via the frequency and amplitude of the AC voltage.

“The new motor could also have technical applications in the future. If we develop the motor further we could possibly use it in the future to drive user-defined chemical reactions. Then, for example, surfaces could be densely coated with such motors. Then you would add starting materials, apply a little AC voltage and the motors produce the desired chemical compound,” Dietz said.