Twisted technique can determine nanoparticle chirality

For the first time, a single, twisted nanoparticle has been accurately measured and characterized in a lab, taking scientists one vital step closer to a time when medicines will be produced and blended on a microscopic scale.

Physicists at the University of Bath in the UK who study materials on the nanoscale made their ground-breaking observations using a new method for examining the shape of nanoparticles in three dimensions. They used this technique, called the hyper-Rayleigh scattering optical activity (HRS OA) technique, to examine the structure of gold (among other materials), resulting in an exceptionally clear image of the 'screw thread' twist in the metal's shape. They report their findings in a paper in Nano Letters.

Understanding the twists within a material (known as its chirality) is vital in industries that produce medicines, perfumes, food additives and pesticides, as the direction in which a molecule twists determines some of its properties. For instance, a molecule that twists clockwise will produce the smell of lemons, while the identical molecule twisting anticlockwise (the mirror image of the lemon-smelling molecule) will produce the smell of oranges.

"Chirality is one of the most fundamental properties of nature. It exists in sub-atomic particles, in molecules (DNA, proteins), in organs (the heart, the brain), in bio-materials (such as seashells), in storm clouds (tornadoes) and in the shape of galaxies (spirals hurling through space)," said Ventsislav Valev, who led the project.

Until now, physicists have relied on 200-year-old optical methods for determining the chiral properties of molecules and materials, but these methods are weak and require large amounts of molecules or materials to work. Through their use of a technique based on powerful laser pulses, Valev and his team at Bath's Centre for Photonics and Photonic Materials have produced a far more sensitive probe for chirality, one that can detect a single nanoparticle as it floats freely in a liquid.

"This is both a record and a milestone in nanotechnology," said Valev. "Pursuing this line of research has been one of the most rewarding achievements in my career."

"The observation by Valev's group is historic, and scientifically it inspires us in our work to synthesize new chiral 3D nanomaterials," said study co-author Ki Tae Nam from Material Science and Engineering at the Seoul National University in Korea.

The potential applications of ultra-sensitive chiral sensing are many. For instance, many pharmaceuticals are chiral. Local pharmacists will be able to harness the technology to mix substances in a completely new way, producing pharmaceuticals from minute droplets of active ingredients rather than from large beakers of chemicals.

"You'll be able to go to the chemist with a prescription and instead of receiving a medicine that has to be mixed from bottles of chemicals and then stored in the fridge for several days, you'll walk away with pills that are mini-labs. Upon cracking the pill, a precise number of micro-droplets will flow through microchannels to mix and produce the needed medicine," predicted Valev.

"For these mini-labs to produce chiral drugs, you'll need to know the number of molecules and catalysts within each micro droplet, as well as their chirality." said PhD student Lukas Ohnoutek, who is the first author of the paper. "This is where our result is really important. We can now aim to produce microdroplets containing a single chiral nanoparticle, to use as catalysts in chemical reactions."

"Looking ahead, we can imagine building up chiral materials and even machines, one nanoparticle at a time, from such microdroplets," added Valev. "To do so would be amazing."

This story is adapted from material from the University of Bath, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.