A machine inspired by an ancient water pump can now operate at the scale of a single molecule.
A team of international researchers has built a tiny motor that uses electric current to spin a helical molecule, while the movement itself can increase the current flowing through the molecule by up to a hundred times.
This discovery opens up a new way to couple mechanical motion and electricity at the smallest scales and opens up new possibilities for molecular electronics.
Scientists have tried for decades to build artificial molecular machines inspired by the motors that power movement in living cells. However, making a molecule rotate predictably under an electric current while maintaining electrical contact with metal electrodes remains a challenge.
The new device demonstrates voltage-controlled rotation with 100 percent directional preference, using a principle that is more than 2,000 years old.
“We have shown that directional rotation can be generated with electric current and that this rotation in turn controls the current. This is a new operating principle for machines at the limit of miniaturization,” said Fabian Pauly, one of the study authors and a professor at the University of Augsburg in Germany.
The Archimedes screw gets a molecular makeover
The researchers were inspired by the Archimedes screw, an ancient device with a spiral blade in a cylinder that lifts water (or solids) when rotated. In the new machine, electrons flowing through a similarly twisted structure create the torque that causes them to rotate.
Instead of relying on an external mechanical tool to move the molecule, the current itself drives the movement. The central component of the motor is a dithioacetyl-functionalized (13)-helicene molecule that Michael Pittelkow’s team at the University of Copenhagen synthesized specifically for the study.
The molecule, which is only a few nanometers in size, can attach itself to gold surfaces via sulfur atoms. At the Weizmann Institute of Science in Israel, researchers led by Oren Tal and Anil Kumar Singh connected individual molecules between two extremely fine gold tips.
These electrodes provided a path for electrical current through the molecule. By adjusting the distance between the tips, the team could stretch or compress the molecular structure, changing the voltage at which current amplification began.
When the researchers applied a voltage, the molecule underwent a cyclic motion with a clear directional preference. By reversing the polarity of the voltage, the direction of rotation was reversed. This gave the team control over the movement of the engine without physically manipulating it.
The movement is driven by current-induced forces: as electrons travel through the helical molecule, they transfer angular momentum to it. The handedness of the molecule determines the direction of rotation, similar to how the threads of a conventional screw determine forward movement.
The researchers showed that the direction can be changed by reversing the voltage polarity. Other researchers have also developed DNA-based molecular nanomachines, but they use a different energy source to generate movement.
The spinning molecule opens a better path for the electrons
The study authors also observed a surprising electrical effect: as soon as the molecule began to move, the current could increase sharply. To understand why, they used quantum mechanical simulations on the LiCCA supercomputer.
Their calculations showed that the molecule conducts electricity very differently depending on the angle of rotation. As it rotates, it can achieve configurations that allow much easier electron flow and increase conductivity by up to two orders of magnitude, or about a hundred times.
“The surprising thing is that it is precisely the positions that the molecule avoids when at rest that conduct the current best. Only rotation makes these positions accessible,” said Léon Martin, one of the researchers and a doctoral student at the University of Augsburg.
Next, the researchers developed a simplified model that reproduced the observed rotation and current increase. Their calculations also predict that the molecule can transition from stepwise motion to continuous rotation above a threshold voltage. Such calculations are part of a broader effort to understand why molecular simulations remain challenging.
“In the experiment you only see the current. Our calculations allow us to take a look at what is happening inside the nanocontact,” said Yuta Ito, one of the study authors.
An engine, not yet a miniature machine shop
The findings could help researchers develop molecular electronic components, spintronic devices that use electron spin to process information, and tiny systems for manipulating fluids. They also provide a way to study how mechanical motion and electrical transport interact at the molecular level.
However, the device remains a laboratory prototype based on a single molecule held between gold electrodes. Its performance in practical devices has not yet been demonstrated, and the proposed applications remain possibilities rather than proven uses.
Further research is needed to determine how the engine behaves under different operating conditions and whether the principle can be integrated into functional molecular technologies.
The study is published in the journal Nature.
