Single nanoparticles could pave the way for medicines on demand

We can now 'see' the twist of a single nanoparticle, floating freely in a liquid. @ Ventsislav Valev and Joel Collins

For the first time, a single, twisted nanoparticle has been accurately measured and characterised 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 who study materials on the nanoscale - that is, molecules 10,000 smaller than a pinhead - made their groundbreaking observations using a new method for examining the shape of nanoparticles in 3D. This technique, called the hyper-Rayleigh scattering optical activity (HRS OA) technique, was used 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.

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) smells 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 Professor 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, Professor 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 discovery was made by Bath's Department of Physics in collaboration with the Department of Chemistry. The researchers' findings are published in Nano Letters.

"This is both a record and a milestone in nanotechnology," said Professor 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 synthesise new chiral 3D nanomaterials," said study co-author Professor Ki Tae Nam from Material Science and Engineering at the Seoul National University in Republic of Korea.

The potential applications for 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." said Professor 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 on 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."

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

Single Nanoparticle Chiroptics in a Liquid: Optical Activity in Hyper-Rayleigh Scattering from Au Helicoids

Lukas Ohnoutek, Nam Heon Cho, Alexander William Allen Murphy, Hyeohn Kim, Dora Maria Răsădean, Gheorghe Dan Pantoş, Ki Tae Nam, and Ventsislav Kolev Valev*

Nano Letters (June 24, 2020)

DOI: 10.1021/acs.nanolett.0c01659

Contact information:

Ki Tae Nam

Professor, Departments of Material Science and Engineering, Seoul National University

Phone: (+82) 02-880-7094

Bioinspired Materials Science research group

Ventsislav Valev

Professor, Department of Physics, University of Bath

Phone: +44 (0) 1225 383307

MultiPhoton NanoPhotonics research group

University of Bath

Spin defects under control

UMass Amherst team discovers use of elasticity to position microplates on curved 2D fluids

The spintronics technology revolution could be just a hopfion away

Scientists watch 2D puddles of electrons emerge in a 3D superconducting material

Lighting the way to folding next-level origami

Energy transmission by gold nanoparticles coupled to DNA structures

A breakthrough that enables practical semiconductor spintronics

SMART discovers the science behind varying performance of different colored LEDs

Optically active defects improve carbon nanotubes

Discovery could help lengthen lifespan of electronic devices