In 2006, the US chemist Paul Rothemund developed a method at the California Institute of Technology with which the thread-like DNA molecule can be folded into numerous different structures. He himself called this technique “DNA Origami” – derived from the Japanese art of origami, in which sheets of paper are folded into three-dimensional structures. Numerous researchers are now using the “DNA origami” technique to construct specific nanostructures.
Scientists from the Technical University of Munich (TUM), the Max Planck Institute for Dynamics and Self-Organization in Göttingen and the University of Oxford have built the first electric nanomotor from DNA molecules using the origami principle. In the journal “Nature” they describe its structure consisting of a base, a platform and a rotor.
The base, which is around 40 nanometers high, is anchored to a glass plate by chemical bonds. Between this base and the rotor arm, which is up to 500 nanometers long, the researchers inserted the so-called platform as an intermediate element, without which the motor could not be set in rotation. It is an indispensable part of the functional principle.
The platform harbors molecular obstacles that impede the movement of the rotor a bit. In order to overcome the obstacles and be able to turn, the rotor has to bend upwards a little bit. The researchers compare the resulting effect with a ratchet that can only be turned if the appropriate energy is supplied.
In the case of the nanomotor, the energy required to turn the rotor is supplied electrically via two tiny electrodes. By choosing the voltage and frequency, the nano motor can be switched on and off and the speed and direction of rotation can be controlled.
Without the supply of energy, the rotor arms move uncontrolled in one direction or the other – driven by random collisions with molecules from the solvent that surrounds the nanomotor.
As soon as an AC voltage is applied, the motor starts to run continuously in the desired direction. The directed movement is created by superimposing the electrical forces with those forces that the rotor experiences on the ratchet obstacle.
“The new motor has mechanical capabilities that have never been achieved before,” says TUM researcher Ramin Golestanian, who was involved in the development. “It can achieve torques in the range of 10 piconewtons by nanometers.” compared to what an average car engine can achieve in terms of torque – that’s 22 orders of magnitude more.
In the case of the DNA motor, however, the researchers are not concerned with mechanical drives, but with technical applications of a completely different kind. “If we further develop the motor accordingly, we could possibly use it to drive chemical reactions in the future,” says Hendrik Dietz, Professor of Biomolecular Science Nanotechnology at TUM.
“Then you could, for example, coat surfaces densely with such motors. Then you add raw materials, apply a little AC voltage and the motors produce the desired chemical compound.”
Natural molecular motors, which have vital tasks in the human body, are the models. For example, what is known as ATP synthase produces the molecule adenosine triphosphate (ATP), which our body uses to temporarily store and transmit energy.
And here the orders of magnitude of the effect can be better compared than with purely mechanical torque. “Our nanomotor can generate more energy per second than is released by splitting two ATP molecules,” notes Golestanian.
