What the research is about
Chirality is known an important property that influences the scent of lemons and the effectiveness of medicines. Chirality refers to the distinction between right-handed and left-handed forms. For example, your right and left hands look very similar, but no matter how you rotate them, they cannot be perfectly superimposed. When a shape has this kind of non-overlapping left-right difference, it is said to have chirality.
In the world of molecules, right-handed and left-handed versions of the same molecule often have very similar basic chemical properties. However, they can behave differently when interacting with living organisms. This is why chirality plays an important role in pharmaceuticals and biological systems.
Interestingly, chirality also affects how electrons behave inside materials. In materials that possess chirality (called chiral materials), electric current can give rise to effects related to the tiny magnetic property of electrons, known as electron spin. As a result, the way electricity flows can depend on the direction of an electron spin. In other words, the "right-handed" and "left-handed" forms can influence electronic behavior.
Because chirality plays such an important role in medicine and daily life, many researchers have focused on developing methods to synthesize chiral substances. However, once a material is synthesized and its chirality is fixed, those properties usually cannot be changed afterward. This led to a long-standing question: Is it possible to change a material's "left" and "right" properties after it has already been made?
To address this challenge, Professor Kouji Taniguchi and his research team at Institute of Science Tokyo (Science Tokyo) focused on a material called molybdenum disulfide (MoS₂). This material does not have chirality (it is achiral), but it allows researchers to control the flow of electricity with high precision.
The team combined MoS₂ with a liquid containing chiral molecular ions and applied a voltage. By carefully adjusting the voltage, they were able to gather chiral ions from the liquid and electrons from the material at the surface. This created a state in which electric current flowed with chiral properties. Their idea-that electricity itself could be used to bring out and control right- and left-handed characteristics at the surface-proved to be correct.
Why this matters
The biggest challenge was proving clearly that chirality was truly being controlled by electricity. Was it simply that molecules were attaching to the surface? Or was the chirality of those molecules actually changing the fundamental electronic properties of the MoS₂ surface where current flows?
To answer this question, the researchers carefully measured key electronic signatures that appear only when chirality is present. These included imbalances in the magnetic orientation of electrons and changes in electrical conduction under a magnetic field. They confirmed that when the applied voltage was changed, these chiral signatures changed as well. This provided the world's first clear demonstration that chirality can be introduced and controlled electrically at the surface of an originally achiral material.
What's next
This achievement opens the door to a new research field known as chiral iontronics, where the motion of ions is used to control the properties of materials. If right- and left-handed characteristics can be switched on demand using electricity, this could lead to next-generation electronic devices that utilize electron spin, highly sensitive sensors, and new information-processing technologies.
The "left-right" differences that once mattered mainly in fragrance and medicine may now play a key role in electronics. This research represents an important step toward connecting molecular science with advanced materials science.
Comment from the researcher
Traditionally, chirality is introduced into materials through chemical reactions. I was honestly not sure at first whether simply gathering molecules at a surface using electricity could truly control chirality. However, as we carefully accumulated experimental evidence, our initial hypothesis gradually turned into confidence. In the end, we were able to demonstrate compelling evidence.
We hope to continue advancing this new approach and move toward a future where chirality can be designed and controlled in ways that were not previously possible.
（Kouji Taniguchi: Professor, School of Science, Institute of Science Tokyo）
