Photonic Effect Graphic
The illustration shows a microplate well in the foreground, while in the background a tested sample receives red laser light and releases twisted blue light. (Image: Ventsislav Valev, Kylian Valev and Lukas Ohnoutek, University of Bath)

Twisted nanoscale semiconductors manipulate light in a new way. This effect could be harnessed to accelerate the discovery and development of life-saving medicines as well as photonic technologies.

The photonic effect could help enable rapid development and screening of new antibiotics and other drugs through automation — essentially, robotic chemists. It offers a new analysis tool for high-throughput screening, a method to analyze vast libraries of chemical compounds. A tiny sample of each compound fills a well on a microplate. The wells can be as small as a cubic millimeter, and a plate the size of a chocolate bar can contain a thousand of them.

One of the key measurements in drug analysis is chirality, or which way the molecule twists. Biological systems, including the human body, typically prefer one direction over the other, a right-handed or left-handed curl. At best, a drug molecule with the wrong twist does nothing, but at worst, it can cause harm. The effect discovered by the researchers allows chirality to be measured in volumes that are 10,000 times smaller than a cubic millimeter.

“The small volumes possible for registration of these effects are the game changing property that enables the researchers to use very small amounts of expensive drugs and collect thousands of times more data,” said Nicholas Kotov, Professor of Chemical Sciences and Engineering at the University of Michigan.

The method relies on a structure inspired by biological designs, developed in Kotov’s lab. Cadmium telluride, a semiconductor commonly used in solar cells, is shaped into nanoparticles resembling short segments of twisted ribbon. These assemble into helices, mimicking the way proteins assemble.

Being illuminated with red light, the small semiconductor helices generate new light that is blue and twisted. The blue light is also emitted in a specific direction, which makes it easy to collect and analyze. The trifecta of unusual optical effects drastically reduces the noise that other nanoscale molecules and particles in biological fluids may cause.

To use these effects in high throughput screening for drug discovery, the nanoparticles assembling into helices may be mixed with a drug candidate. When the nanohelices form a lock-and-key structure with the drug, simulating the drug target, the twist of the nanohelices will change dramatically. This change in the twist can be measured through the blue light.