Measuring molecules with twisted laser light

New laser system can measure the detail of left or right-handed molecules
19th April 2018

Researchers at the University of Bath have developed a new laser and grating system to measure the structure of molecules.

The technique can be used to probe the structure and purity of molecules in pharmaceuticals, agricultural chemicals and food more easily and cheaply than existing methods.

The team from the Centre for Photonics and Photonic Materials, and the Centre for Nanoscience and Nanotechnology at the University of Bath used a special white-light laser built in-house and directed it through several optical components to put a twist on the beam. The twisted laser beam then hits a nanoscopic, U-shaped gold grating which serves as a template for the light, further twisting the beam to the left or right. This deflects the beam in many directions and further splits it into its constituent wavelengths across the colour spectrum.

By carefully measuring the deflected light, scientists can detect tiny differences in intensity across the spectrum which tells them about the structure of the molecule.

Working with colleagues at the University of Cambridge and University College London, the technique relies on the fact that many biological and pharmaceutical molecules can be either ‘left-handed’ or ‘right-handed’ mirror images of each other, and this ‘chirality’ sometimes changes their properties drastically

“At the moment chiral sensing requires high molecular concentrations because you’re looking for tiny differences in how the light interacts with the target molecule,” said Christian Kuppe, the PhD student who conducted the experiments.

“By using our gold gratings we aim to use a much smaller amount of molecules to conduct a very sensitive test of their handedness. The next step will be to continue to test the technique with a range of well-known chiral molecules.

“We hope that this will become a valuable way to perform really important tests on all sorts of products including pharmaceuticals and other high-value chemicals.”

“There’s a great deal of scientific excitement about miniaturisation and working on nano-sized dimensions at the very small scale. However, in the rush to go as small as possible, some opportunities have been overlooked. Working with chiral nano-gratings is a great example of that,” said Dr Ventsislav Valev, who oversaw the work.

The Centre for Photonics and Photonic Materials is formed by around 30 academics, postdoctoral researchers and PhD students from the Department of Physics, who work on cutting-edge research in Photonics.