Scientists Unveil Groundbreaking Single-Molecule Motor: A Leap Forward in Nanotechnology

An international research collaboration has achieved a remarkable feat, developing a functional motor from a single molecule that mimics the ancient Archimedean screw. This revolutionary device, powered by electrical current, exhibits an astonishing tenfold increase in conductivity during rotation, a phenomenon now elucidated by researchers at the University of Augsburg.

The Dawn of Molecular Machines: A Tiny Engine with Big Implications

In a breakthrough that blurs the lines between chemistry and engineering, an international team of scientists has engineered a functional motor at the molecular level. This minuscule machine, inspired by the elegant design of the Archimedean screw, operates by harnessing the power of electrical current to induce rotation in a single molecule. The implications of this achievement are profound, opening doors to novel applications in molecular electronics, spintronics, and microfluidics.

The core of this innovation lies in a specially designed helical molecule, a type of molecule known as a helicene. These molecules possess a unique three-dimensional, spiral structure, akin to a microscopic screw thread. When suspended between two atomically sharp gold tips, acting as electrodes, and subjected to an electrical voltage, the molecule begins to spin. What truly captivates researchers is the dramatic surge in electrical current observed once the molecule reaches a critical rotational speed. Under specific experimental conditions, this current can amplify by a staggering factor of up to 100.

Unraveling the Mystery: The Archimedean Screw at the Nanoscale

The inspiration for this molecular motor can be traced back over two millennia to the ingenious invention of the Archimedean screw. This ancient device, still employed today in applications like pumping systems and water treatment plants, revolutionized the transportation of fluids. The helical geometry of the molecule employed in this new research mirrors this time-tested principle. However, instead of water, the molecular screw facilitates the flow of electrons, which in turn imparts rotational motion. The groundbreaking results of this research have been published in the prestigious scientific journal, Nature.

How Does a Single-Molecule Motor Work?

The molecular engine is built upon a specific class of molecules called helicenes. Their defining characteristic is their unique spatial arrangement: they are constructed in a spiral fashion. Depending on their specific configuration, these molecular spirals can be either right-handed or left-handed, much like the threads of a screw.

A dedicated team, led by Michael Pittelkow at the University of Copenhagen, synthesized a specialized helicene molecule for this experiment. This molecule, measuring only a few nanometers in size, is equipped with sulfur atoms. These atoms serve as crucial anchoring points, allowing the molecule to bind to gold surfaces.

The critical step of isolating and manipulating individual molecules was achieved by a team at the Weizmann Institute of Science in Israel, under the guidance of Oren Tal and Anil Kumar Singh. They succeeded in precisely positioning these single helicene molecules between two gold tips, so fine that they are atomically precise. These gold tips served a dual purpose: they acted as electrodes, allowing researchers to apply an electrical voltage, and as sensors, enabling the measurement of the current flowing through the molecule.

The experimental setup allowed for precise control over the distance between the gold tips. This fine-tuning enabled researchers to either stretch or compress the molecule, thereby investigating its electrical properties under varying conditions. The most remarkable observation emerged when an electrical voltage was applied: the electrons flowing through the molecule transferred angular momentum to its helical structure. This transfer of momentum initiated the molecule’s rotation. Crucially, above a certain voltage threshold, this rotation became continuous, effectively creating a molecular motor.

Steering the Nanoscale Revolution: Controlling Rotation with Voltage

The research team not only demonstrated directed rotation but also achieved the unprecedented ability to control its direction. This control was elegantly accomplished by simply reversing the polarity of the applied electrical voltage. When electrons flowed in the opposite direction, the preferred direction of the molecule’s rotation also reversed. The specific direction of rotation for a given current direction was found to be intrinsically linked to the molecule’s inherent helical structure.

While electrically driven molecular motors are not entirely novel – with earlier research in 2011 demonstrating the manipulation of molecules on a surface using a scanning tunneling microscope tip – this new experimental setup presents a significant advancement. A key distinction is that the rotating molecule remains in continuous electrical contact between two metal electrodes. According to the University of Augsburg, this research marks the first demonstration of a current-driven molecular motor with a controllable direction of rotation.

The Enigma of the Hundredfold Current Surge: Unveiling the Mechanism

The most striking and puzzling observation from the experiments was the dramatic surge in electrical current. This amplification could not be solely attributed to the applied voltage; it strongly suggested that the rotation itself was actively influencing electron transport.

To unravel this complex interplay, researchers at the University of Augsburg employed sophisticated quantum mechanical computer simulations. Fabian Pauly and his doctoral students, Léon Martin and Yuta Ito, utilized the high-performance computing cluster LiCCA for their calculations.

The simulations revealed a profound correlation between the molecule’s rotational angle and its electrical conductivity. Specific angular orientations of the molecule facilitated significantly higher electron transport compared to others. Intriguingly, these highly conductive orientations were not typically adopted by the molecule in its quiescent, stationary state. It was the act of rotation that made these favorable positions accessible.

"The surprising aspect is that precisely those orientations that the molecule avoids at rest conduct electricity best. Only the rotation makes these positions accessible," explained Léon Martin in a press release from the University of Augsburg on October 22, 2026.

This means that the rotation can enhance the conductivity of the molecular junction by up to two orders of magnitude, translating to a factor of 100. The phenomenon is characterized by a reciprocal relationship: the electrical current initiates the molecular motion, and this motion, in turn, modulates the current flow. It is important to note that this process does not generate additional electrical energy. The measurements indicate that with an appropriately applied voltage, significantly more current can pass through the junction. However, a hundredfold increase in overall efficiency has not been demonstrated.

The significance of mechanical properties in individual molecules for electronics is further underscored by other research. For instance, scientists at the University of Cambridge have investigated the stiffness of individual molecules within organic semiconductors.

Bridging Experiment and Simulation: A Holistic Understanding

The movement of a motor just a few nanometers in size cannot be directly observed with a conventional camera, unlike macroscopic machines. Therefore, researchers focused on analyzing the electrical behavior of the molecule situated between the gold tips.

The experimental measurements provided crucial evidence for directed rotation and the accompanying current surge. The subsequent computer simulations were instrumental in deciphering the intricate processes occurring within the molecular junction.

"In the experiment, one only sees the current. Our calculations allow a glimpse into what is happening inside the nanocontact. It was only through the close collaboration of experiments and theory across multiple countries that the mystery of the current surge could be solved," stated Yuta Ito from the University of Augsburg.

Following this, Per Hedegård from the Niels Bohr Institute in Copenhagen and Jing-Tao Lü from the Huazhong University of Science and Technology in Wuhan developed a simplified physical model. This model effectively reproduced both the observed rotation and the significant current increase, providing a robust explanation for the phenomenon.

This collaborative effort seamlessly integrates experimental measurements with quantum mechanical calculations, offering a comprehensive explanation for how the electrical conductivity of a molecular junction can be influenced not only by its structural configuration but also by its dynamic motion.

Future Horizons: Potential Applications of the Molecular Motor

While the current research represents a groundbreaking scientific achievement, practical applications of this molecular motor are still some way off. The molecular machine currently operates under highly controlled laboratory conditions, precisely positioned between two extremely fine gold contacts. Nevertheless, the researchers have identified several promising avenues for future applications. These include molecular electronics, spintronics, and microfluidic systems.

Molecular electronics aims to utilize individual molecules as fundamental components in electronic circuits. Spintronics, on the other hand, extends beyond the electrical charge of electrons to incorporate their intrinsic angular momentum, known as spin, for information processing. Microfluidic systems are designed for the precise movement and control of minute quantities of liquids.

The research team has not yet unveiled specific component designs for these applications. The current focus remains on deepening the fundamental understanding of the underlying physical processes.

"We have demonstrated that directed rotation can be generated with electrical current, and that this rotation, in turn, controls the current. This represents a novel operating principle for machines at the extreme limit of miniaturization," explained Fabian Pauly.

This pioneering work signifies a monumental step forward in the field of nanotechnology, offering a glimpse into a future where machines are built not from gears and circuits, but from the very building blocks of matter. The ability to precisely control and harness molecular motion opens up a universe of possibilities for innovation across various scientific and technological domains.