Many molecules exist in two forms that are mirror images of each other, such as left and right hands. Although these molecular twins may appear nearly identical, they can behave dramatically differently, especially in biological systems and medicines. Distinguishing these enantiomers (also called chiral molecules) remains a major scientific and technological challenge.
One way to understand molecular handedness is to think about screws and nuts. Right-handed threads will fit right-handed threads, but left-handed threads will not. The researchers now show that a specially shaped light can act as a similar type of threaded probe, interacting differently with molecules depending on their handedness.
Adding a twist to laser light
Scientists at Tata Institute of Fundamental Research, Indian Institute of Technology Mumbai, and Indian Institute of Technology Hyderabad have designed a light that does more than just rotate. It also twists when moving forward.
When this structured light hits a chiral molecule, the interactions change depending on how the “twist” of the light matches the molecule’s natural handedness. This creates a measurable difference that can be used to identify which mirror image form is present.
break down molecules into detectable fragments
The experiment was conducted at the TIFR Hyderabad laser facility. The researchers irradiated a gaseous sample of R-camphor or S-camphor, a well-known chiral molecule, with ultrashort laser pulses (hundreds of femtoseconds) with carefully controlled spin and twist.
The laser pulse broke the molecules into charged fragments. The scientists then examined these fragments using a time-of-flight mass spectrometer, an instrument that identifies ions by measuring the time it takes them to reach a detector. Lighter debris arrives faster than heavier debris.
The research team observed an important pattern. The number of fragments produced varies depending on the combination of light twisting and molecular handedness. By simply comparing the number of fragments, the researchers were able to distinguish between the two mirror forms.
A simple way to detect the handedness of a molecule
Traditional methods for detecting chirality often measure very small differences in the way molecules absorb light. Other techniques track the direction in which the electrons are emitted. These approaches may require complex equipment, precise alignment, angle measurements, or coincidence detection.
Newer techniques instead determine chirality directly through ion signals. This reduces the need for complex measurements while also increasing sensitivity.
Study molecules without external interference
The researchers studied the molecules in the gas phase, separating them from external influences such as solvents and surfaces. This allowed us to more directly observe the underlying interactions between structured light and molecular shape.
The twisted light also highlighted the differences between the two enantiomers. As a result, the signal was larger than that typically produced by traditional optical methods.
Matching twisted light and chiral molecules
As a result, new ways of “matching the threads” between light and matter have been introduced. By using twisted laser beams as probes, scientists may be able to more easily and precisely identify the handedness of molecules.
This method could create new opportunities in chemistry, biology, and pharmacy. In these fields, choosing the correct enantiomer is essential because two mirror-image versions of the same molecule can have very different biological or medical effects.
