Nanoscale synthetic rotary motors do mechanical work

A research team led by the Technical University of Munich (TUM) has succeeded for the first time in producing a molecular electric motor using the DNA origami method. The tiny machine made of genetic material self-assembles and converts electrical energy into kinetic energy. The new nanomotors can be turned on and off, and researchers can control the rotation speed and direction of rotation.

Whether in our cars, drills, or automatic coffee grinders, motors help us perform jobs in our daily lives to accomplish a wide variety of tasks. On a much smaller scale, natural molecular motors perform vital tasks in our bodies. For example, a motor protein known as ATP synthase produces the molecule adenosine triphosphate (ATP), which our bodies use for short-term energy storage and transfer.

While natural molecular motors are essential, it has been quite difficult to recreate motors on this scale with roughly similar mechanical properties to natural molecular motors like ATP synthase. A research team has now built a nanoscale molecular rotating motor using the DNA origami method. The team was led by Hendrik Dietz, Professor of Biomolecular Nanotechnology at TUM, Friedrich Simmel, Professor of Physics of Synthetic Biological Systems at TUM, and Ramin Golestanian, Director of the Max Planck Institute for Dynamics and Self-Organization.

A self-assembled nanomotor

The new molecular motor consists of DNA – genetic material. The researchers used the DNA origami method to assemble the engine from DNA molecules. This method was invented by Paul Rothemund in 2006 and was later developed by the TUM research team. Several long single strands of DNA serve as the base to which additional DNA strands attach as homologs. DNA sequences are selected so that the attached strands and folds create the desired structures.

“We have advanced this manufacturing method 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,” says Dietz.

The new DNA material nanomotor consists of three components: a base, a platform and a rotor arm. The base is approximately 40 nanometers tall and is attached to a solution glass plate via chemical bonds to a glass plate. A rotor arm with a length of up to 500 nanometers is mounted on the base so that it can rotate. Another component is crucial for the engine to perform as intended: a platform located between the base and the rotor arm. This platform contains obstacles that influence the movement of the rotor arm. To pass obstacles and turn, the rotor arm must bend upwards a little, like a ratchet.

Targeted movement thanks to alternating voltage

Without energy input, the rotor arms of the motors move randomly in one direction or the other, driven by random collisions with molecules of the surrounding solvent. However, as soon as an alternating voltage is applied via two electrodes, the rotor arms rotate purposefully and continuously in one direction.

“The new motor has unprecedented mechanical capabilities: it can reach torques of the order of 10 piconewton times a nanometer. And it can generate more energy per second than is released when two molecules of ATP are separated,” says Ramin Golestanian, who led the theoretical analysis. of the engine mechanism.

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 underlying mechanism achieves a so-called “blinking Brownian ratchet”. Researchers can control the speed and direction of rotation via the direction of the electric field and also via the frequency and magnitude of the alternating voltage.

“The new engine could also have technical applications in the future. If we develop the engine further, we could possibly use it in the future to drive user-defined chemical reactions inspired by the way the ATP synthase makes ATP spin-driven. Then, for example, surfaces could be densely covered with such motors. Then you would add starting materials, apply a small alternating voltage, and the motors would produce the desired chemical compound,” explains Dietz.

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