Optical methods for distinguishing left-handed from right -handed molecules outpace in their speed the chemical methods and hold a potential for detection of chiral biomarkers. However, traditional optical methods face a number of challenges, including the need for large sample sizes to accurately identify left-handedness or right-handedness, which can get very expensive.
The new research introduces a completely new structure of light: the electric field of the light traces out a chiral curve over time, with a handedness that changes as you go around the beam. This spatial variation of handedness then creates a ‘chiral vortex’.
When chiral molecules interact with this vortex, they emit photons through a process called high-harmonic generation (winner of the Nobel Prize for Physics 2023) in a recognisable pattern that can be spotted by an experiment.
When a molecule's handedness is switched, the corresponding pattern of chirality rotates in space. This is picked up by readings in a rotating pattern of colour that distinguishes the handedness of the molecule. The far left is a left-handed molecule, while the one on the right is right-handed, both with very specific patterns.
When the molecule’s handedness is switched, the corresponding pattern rotates in space. This allows for a more accurate detection of the handedness of the sample, when compared to standard methods as they rely on the comparatively weak magnetic field of the light which produces a far weaker signal.
Dr Nicola Mayer, postdoctoral researcher in the group of Prof. Olga Smirnova at the Max Born Institute and incoming Marie Skłodowska-Curie Actions Research Fellow at King’s College London, and the first author of the study, said “Traditional measures of chirality have struggled to identify the concentration of right- and left-handed molecules in samples containing almost equal amounts of both. With our new method, a tiny excess in the concentration of either mirror twin can be detected, such as when the sample is 49% right-handed and 51% left-handed. It can find applications in detection of chiral biomarkers.”
“By focusing on the detection of a rotating pattern of the light emitted by the molecules, it is a lot easier to sense and interpret minor differences in the handedness of dilute samples. Furthermore, the vortex nature of the laser beam we designed means the signals we receive are robust against the common pitfalls of chirality experiments in the lab, like fluctuations in the intensity of the light, empowering more people to carry out this work.
