Polarized light waves, which spin clockwise or counterclockwise as they travel, interact differently with molecules based on their direction. This property, known as chirality or handedness, could help identify and sort specific molecules for biomedical applications. However, researchers have had limited control over the direction of these waves—until now.

A team of electrical engineering researchers from Penn State and the University of Nebraska-Lincoln (UNL) has developed an ultrathin optical element using metamaterials that can control the direction of polarized electromagnetic light waves. This advancement allows researchers to direct the light's chirality and identify the chirality of molecules by observing how polarized light interacts with them. The team's findings were published in Nature Communications.

Chirality involves mirror images, like left and right hands, explained Christos Argyropoulos, associate professor of electrical engineering at Penn State and co-corresponding author of the paper. In physics, chirality influences the spin direction of light waves.

Argyropoulos and his team fabricated an optical element, similar to a glass slide, using a forest of tiny, antenna-like nanorods that form a metamaterial—engineered to have properties not typically found in nature. These nanorods, when viewed at the nanoscale, resemble the letter "L."

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

The researchers at UNL employed an innovative fabrication method called glancing angle deposition to create the optical element from silicon.

"Silicon does not substantially dissipate the incident light, which was problematic with metal used in previous attempts," said Ufuk Kilic, a research professor at UNL and co-corresponding author of the paper. "Silicon also allowed us to adjust the shape and length of the nanopillars on the platform, enabling us to change how we control the light."

Identifying the chirality of molecules is crucial in biomedicine, particularly for pharmaceutical drugs, which can have right- or left-handed chirality, Argyropoulos explained. While a right-handed molecule can effectively treat disease, the same molecule with a left-handed structure can be toxic to healthy cells.

A classic example is thalidomide, a drug with a chiral structure prescribed for morning sickness between 1957 and 1962. The right-handed molecule could alleviate nausea, but the left-handed molecule was highly toxic to developing fetuses, causing birth defects in thousands of babies. The new optical element can quickly image the molecular structure of pharmaceuticals, helping scientists understand drug behavior nuances.

Additionally, the optical element can create right- or left-handed electromagnetic waves, essential for classical and quantum communication systems like encrypted Wi-Fi and cell phone service.

"Previously, optical communication systems required large, bulky devices that only operated at one frequency," Argyropoulos said. "This new optical element is lightweight and easily tunable to multiple frequencies."