- The micro-motor uses electric current to drive the rotation of helical molecules, amplifying the current by up to 100 times.
- The device demonstrates voltage-controlled rotation with a 100% directional preference.
- The conductivity of the molecules is optimal when stationary, with rotation allowing them to reach their best position.
- The research may advance the development of molecular electronic components and microfluidic systems.
Inspired by ancient water pumps, the machine can now operate at the single-molecule scale. An international team of researchers has built a micro-motor that uses electric current to drive the rotation of helical molecules, a motion that can amplify the current flowing through by up to 100 times. This discovery establishes a new method for coupling mechanical motion with electricity at the smallest scales, opening new possibilities for molecular electronics. Scientists have spent decades trying to build artificial molecular machines inspired by the movement inside biological cells. However, achieving predictable rotation of molecules under current while maintaining electrical contact with metal electrodes has remained a challenge.
This new device demonstrates voltage-controlled rotation with a 100% directional preference, utilizing a principle that dates back over 2,000 years.
Principle of Voltage-Controlled Rotation
Fabian Pauli, one of the research authors from the University of Augsburg, stated, "We have demonstrated that current can be used to generate directional rotation, which in turn controls the current. This is a new operational principle for machines at the limits of miniaturization." The researchers drew inspiration from the design of Archimedes' screw, an ancient device with helical blades that can lift water or solids when rotated. In this new machine, electrons flowing through a similarly twisted structure generate the torque that causes it to rotate. This motion is no longer reliant on external mechanical tools but is driven by the current itself.
The core component of the motor is a helical molecule with disulfide acetyl functional groups (13), specially synthesized by Michael P. Petkov's team at the University of Copenhagen. This molecule, only a few nanometers in size, can attach to a gold surface via sulfur atoms. Researchers from the Weizmann Institute of Science in Israel, led by Oren Tal and Anil Kumar Singh, connected a single molecule between two extremely fine gold tips. These electrodes provide a pathway for the current to flow through the molecule. By adjusting the distance between the tips, the team can stretch or compress the molecular structure, altering the voltage at which current amplification begins.
When the researchers applied voltage, the molecule underwent a clearly preferred directional cyclic motion. Reversing the polarity of the voltage reversed the direction of rotation. This allowed the team to control the motor's movement without physical manipulation. The motion is driven by forces induced by the current: as electrons pass through the helical molecule, they transfer angular momentum to it. The chirality of the molecule helps determine the direction of rotation, similar to how the threads of a traditional screw dictate its advancement. The researchers demonstrated that reversing the voltage polarity could change the direction.
Astonishing Effects of Molecular Conductivity
Other researchers have also developed DNA-based molecular nanomachines, although they use different energy sources to generate motion. The authors of this study also observed an astonishing electrical effect: once the molecule began to move, the current could rise sharply. To understand the reasons behind this, they conducted quantum mechanical simulations on the LiCCA supercomputer. Their calculations showed that the conductivity of the molecule varies dramatically at different rotational angles. As it rotates, it can access configurations that allow electrons to flow more easily, leading to an increase in conductivity by up to two orders of magnitude, approximately 100 times.
One of the researchers, Leon Martin, stated, "Surprisingly, the best conductivity occurs when the molecule is in positions that it avoids when stationary. Only rotation can make these positions accessible." Next, the researchers developed a simplified model that reproduced the observed rotation and current amplification. Their calculations also predicted that when the voltage exceeds a certain threshold, the molecule could transition from gradual motion to continuous rotation. These calculations are part of a broader effort to understand why molecular simulations remain challenging. One of the study's authors, Yuta Ito, remarked, "In experiments, you can only see the current.
Our calculations allow us to glimpse what happens inside the nano contacts."
Potential for Future Applications
These findings may assist researchers in developing molecular electronic components, spintronic devices (which use electron spin to process information), and microfluidic manipulation systems. They also provide a way to study the interaction between mechanical motion and electrical transport at the molecular scale. However, the device remains a laboratory prototype based on a single molecule between gold electrodes, and its performance in practical devices has yet to be established, with proposed applications still being possibilities rather than proven uses. Further research is needed to determine the motor's behavior under different operating conditions and whether this principle can be integrated into functional molecular technologies.
The study was published in the journal Nature.
Item Specification Core Molecule Disulfide acetyl functionalized helical molecule Current Amplification Up to 100 times Rotation Direction Control 100% directional preference
Potential Impact of Micro-Motor Technology
This research demonstrates how to achieve the coupling of mechanical motion and current at the molecular scale, providing new insights for advancements in molecular electronics. Through the ancient principle of the Archimedes screw, researchers successfully converted current into rotational motion and further amplified the current, which is significant for the future development of electronic components and microfluidic systems. Although still in the laboratory prototype stage, these findings pave the way for further exploration of functional molecular technologies, showing broad potential for future applications in the field of nanotechnology.