Scientists Create a Single-Molecule Screw That Rotates Using Electric Current

Scientists have demonstrated a miniature molecular machine that uses electric current to generate controlled rotational movement. Inspired by the ancient Archimedes screw, the device applies a familiar mechanical principle at a scale millions of times smaller than everyday machines.

The research explores how electrons travelling through a specially designed helical molecule can transfer angular momentum and set the molecule into rotation. Researchers also demonstrated that reversing the electrical voltage can reverse the direction of rotation.

The findings could help advance molecular electronics, nanoscale machinery and the study of physical processes at the atomic level. The work also highlights how electrical conductivity and mechanical movement can be linked within a single molecule.

What Is a Molecular Motor?

A molecular motor is a system that converts energy into directed movement at the molecular scale. Nature already uses such mechanisms inside living cells, where molecular motors perform essential tasks by moving cellular components and transporting materials.

Scientists have spent decades trying to develop artificial versions of these biological machines. The goal is to reproduce controlled movement using individual molecules rather than conventional mechanical components.

Research into molecular machines received major recognition in 2016, when the Nobel Prize in Chemistry was awarded to Jean-Pierre Sauvage, Sir J. Fraser Stoddart and Bernard L. Feringa for their work on the design and synthesis of molecular machines.

The latest research builds on this broader field by demonstrating how an electrical current can directly drive the rotation of a molecule held between two metal electrodes.

How the Molecular Archimedes Screw Works

The design takes inspiration from the Archimedes screw, a device traditionally used to lift water from a lower level to a higher one through a rotating helical structure.

In the new molecular system, the researchers adapted the screw's helical geometry to control movement at an extremely small scale. Instead of relying on water or a conventional mechanical drive, the device uses electrons flowing through the molecule.

As electrons pass through the helical structure, they transfer angular momentum to the molecule. This interaction generates rotational movement, somewhat comparable to how wind transfers energy to a turbine.

The direction of rotation depends on the electrical voltage's polarity and the molecule's helical structure. Changing the polarity reverses the direction of rotation, providing a way to control the machine electrically.

This approach offers a different route to operating molecular machinery without relying on a scanning tunnelling microscope tip to drive movement mechanically.

Inside the Device: A Helical Molecule Between Gold Electrodes

The machine is built around a specially synthesised helical molecule. The research team led by Professor Michael Pittelkow at the University of Copenhagen developed the molecule for the study.

Sulphur atoms allow the molecule to attach to gold surfaces, enabling researchers to establish an electrical connection through the molecular structure.

At Israel's Weizmann Institute of Science, a team led by Professor Oren Tal and Dr Anil Kumar Singh positioned individual molecules between two extremely fine gold electrodes.

By carefully adjusting the distance between the electrodes, the researchers could stretch or compress the molecular screw. This arrangement enabled them to investigate how the molecule's structure and electrical conditions affected its movement.

The molecule itself measures only a few millionths of a millimetre, placing the device firmly within the world of nanoscale engineering.

Voltage Controls the Direction of Rotation

Measurements showed that applying an electrical voltage could trigger the molecule's rotation. The direction was controllable: reversing the voltage polarity reversed the direction of movement.

The researchers also observed a transition to continuous rotation once the voltage crossed a certain threshold.

This is an important distinction because a practical molecular motor needs more than the ability to move. Its movement must be controllable and reproducible under defined operating conditions.

The findings demonstrate a way to combine electrical input and directed mechanical movement within a single molecular structure attached to metal electrodes.

Further research will be needed to determine how reliably such devices can operate under different conditions and how their movement could be incorporated into more complex systems.

Why Does Rotation Improve Electrical Conductivity?

One of the study's most interesting findings concerns the relationship between the molecule's movement and its ability to conduct electricity.

Researchers at the University of Augsburg investigated this behaviour using quantum-mechanical simulations performed on the LiCCA supercomputer. The team included Professor Fabian Pauly and doctoral researchers Léon Martin and Yuta Ito.

Their calculations showed that the molecule's electrical conductivity depends strongly on its rotational position. During rotation, conductivity can increase by as much as two orders of magnitude, equivalent to a factor of up to 100.

The explanation is linked to the relationship between molecular geometry and electron transport. Certain molecular configurations that are less accessible when the molecule is stationary can become accessible during rotation, allowing electrical current to pass more efficiently.

This means that the molecule's movement does not simply result from the electrical current. Its changing position also influences how readily it conducts electricity.

The discovery reveals a close feedback relationship between electrical transport and mechanical motion at the molecular scale.

International Research Collaboration Helped Explain the Mechanism

The study brought together experimental and theoretical researchers from several countries.

In addition to the teams at the University of Copenhagen, the Weizmann Institute of Science and the University of Augsburg, theoretical researchers Per Hedegård of the Niels Bohr Institute in Copenhagen and Jing-Tao Lü of Huazhong University of Science and Technology in Wuhan contributed to the work.

Their simplified theoretical model reproduced the experimentally observed rotation and the increase in electrical current.

This collaboration was important because experimental measurements reveal observable quantities, such as electrical current, but do not necessarily show every process taking place inside a molecular junction.

Quantum-mechanical calculations helped researchers connect the measured current with the molecule's internal movement and explain why changes in orientation affect conductivity.

Combining experimental evidence with theoretical modelling therefore provided a more complete picture of how the molecular motor operates.

Potential Applications in Molecular Electronics and Nanotechnology

Although the device remains a research achievement rather than a ready-to-use commercial product, the findings could contribute to several areas of science and engineering.

Molecular Electronics

The demonstrated link between molecular rotation and electrical conductivity could help researchers develop electronic components whose behaviour changes with molecular movement.

Such systems may eventually support new ways of controlling electrical signals at extremely small scales.

Spintronics

Spintronics explores the use of electron spin alongside electrical charge to process and store information. Understanding how electrons interact with a helical molecular structure could provide useful insights for future research in this field.

However, practical spintronic applications would require additional investigation and validation.

Nanoscale Machinery

Artificial molecular motors could eventually become components in more complex nanoscale systems. Electrically controlled rotation offers one possible method for operating such components.

Microfluidics and Fundamental Research

Molecular machines may also help researchers investigate how movement, energy transfer and electron transport behave in confined environments. Potential applications in microfluidic systems remain exploratory and would depend on further engineering developments.

The immediate significance of the work lies in demonstrating a controllable operating principle, rather than establishing that the technology is already suitable for industrial use.

Research Funding and Institutional Support

The work at the University of Augsburg received funding from the German Research Foundation through Collaborative Research Centre SFB 1585, project number 492723217. The computational work used the university's LiCCA supercomputer under DFG project number 499211671.

The wider collaboration also received support from organisations including the European Research Council, the Israel Science Foundation, the Minerva Foundation, the Villum Foundation, the Novo Nordisk Foundation, the Independent Research Fund Denmark and research funding agencies in China.

This international support reflects the interdisciplinary nature of molecular-machine research, which combines chemistry, experimental physics, quantum theory and advanced computing.

Conclusion

The development of an electrically driven molecular Archimedes screw demonstrates how a principle from classical engineering can inspire machinery at the molecular scale.

By using electrons to generate controllable rotation, the researchers have shown that electrical transport and mechanical movement can be closely connected within a single molecule. Their findings also explain why rotation can substantially improve the molecule's conductivity.

The work could inform future research in molecular electronics, spintronics and nanoscale engineering. While practical applications remain a longer-term prospect, the study offers an important step towards understanding and controlling machines at the smallest scales.

Sources By Agencies