Shining light on molecules: L-shaped metamaterials can control the direction of light

Polarized light waves rotate clockwise or counterclockwise as they travel, with one direction behaving differently than the other as it interacts with molecules. This direction, called chirality or handedness, could provide a way to identify and sort specific molecules for use in biomedical applications, but researchers have had limited control over the direction of the waves — until now.

Using metamaterials, a team of electrical engineering researchers from Penn State and the University of Nebraska-Lincoln (UNL) created an ultrathin optical element that can control the direction of polarized electromagnetic light waves. This new control allows researchers to not only direct the chirality of light, but also identify the chirality of molecules by determining how polarized light interacts with them.

Identifying the chirality of molecules can reveal critical information about how they will interact with other systems, such as whether specific drugs will help heal diseased or damaged tissue without harming healthy cells. The researchers have published their findings in Nature Communications.

Chirality refers to mirror images, like left and right hands coming together in a handshake, explained Christos Argyropoulos, associate professor of electrical engineering at Penn State and co-corresponding author on the paper. In physics, among other responsibilities, chirality affects the direction light waves rotate.

Argyropulos and his colleagues fabricated an optical element, similar to a glass slide, that uses a forest of tiny, antenna-like nanorods, which together create a metamaterial, or material engineered to have specific properties that normally don’t. found in nature – able to control rotation. of light. Metamaterial nanorods appear to be shaped like the letter “L” when viewed at the nanoscale.

“When light-matter interaction is mediated by metamaterials, you can image a molecule and identify its chirality by inspecting how chiral light interacts with it,” Argyropoulos said.

Researchers at UNL used an emerging fabrication approach called viewing angle deposition to fabricate the optical element from silicon.

“Silicon does not substantially scatter the incident light that was problematic with the metal we used in previous attempts to create the element,” said Ufuk Kilic, a research professor at UNL and co-corresponding author on the paper. “And the silicon allowed us to adjust the shape and length of the nanopillars on the platform, which in turn allows us to change the way we control the light.”

Identifying the chirality of molecules could have far-reaching implications in biomedicine, especially pharmaceutical drugs, which sometimes have right- or left-handed chirality, Argyropoulos explained. While a right-handed molecular structure may be effective in treating disease, the same molecule with a left-handed structure may be toxic to healthy cells.

Argyropulos cited the classic example of thalidomide, a drug with a chiral structure that was recommended to women to treat morning sickness between 1957 and 1962. The right-handed molecule could soothe nausea but was highly toxic to developing fetuses and caused birth defects. birth for thousands of babies around the world.

The optical element, Argyropulos said, can quickly image the molecular structure of pharmaceuticals, allowing scientists to better understand the nuances of drug behavior.

Additionally, the optical element can be used to create right- or left-handed electromagnetic waves, Argyropulos said, which are necessary for the development and maintenance of classical and quantum communication systems, such as encrypted Wi-Fi service and mobile phones.

“Before, for optical communication systems, you needed big, bulky devices that only worked on one frequency,” Argyropulos said. “This new optical element is lightweight and easily tunable at multiple frequencies.”