Boron 2D material may surpass graphene in improving a variety of next-gen technologies.

Graphene has been this decade's star of materials development, lending itself to everything from cancer detection to stronger concrete. But a new and improved two-dimensional material is making its presence known in the world of nanomaterials – borophene.

First synthesized in 2015, borophene is the nano-thin 2D version of boron that is more conductive, lighter, stronger, and more flexible than graphene.

In addition, researchers at Penn State have boosted the material's potential by enabling it to interact in unique ways with different biological units, such as cells and protein precursors, which could make for high-resolution sensors and hardy, implantable medical devices.

"Borophene is a very interesting material, as it resembles carbon very closely including its atomic weight and electron structure but with more remarkable properties. Researchers are only starting to explore its applications," said Dipanjan Pan, team leader. "To the best of our knowledge, this is the first study to understand the biological interactions of borophene and the first report of imparting chirality on borophene structures."

The chirality is what makes it unique, induced via a method never before used on borophene. Chirality refers to similar but not identical physicality, like left and right hands, where biological or chemical units exist as near-mirror images of each other, but the two versions cannot be perfectly matched.

Borophene's building blocks can be configured to "tune" different properties, giving researchers the ability to design materials that emphasize various useful functions.

"Since this material has remarkable potential as a substrate for implantable sensors, we wanted to learn about their behavior when exposed to cells," Pan said. "Our study, for the first time ever, showed that various polymorphic structures of borophene interact with cells differently and their cellular internalization pathways are uniquely dictated by their structures."

Dipanjan Pan

Study authors, led by Professor Dipanjan Pan, left, with Teresa Aditya, postdoctoral researcher in nuclear engineering, and David Skrodzki, graduate research assistant in materials science and engineering, in Pan's lab.

Synthesizing borophene

The researchers synthesized borophene platelets – mimicking blood cell biology – which involved exposing a powdered version of the material in a liquid to heat or pressure until they combined into the desired product.

"We made the borophene by subjecting the boron powders to high-energy sound waves and then mixed these platelets with different amino acids in a liquid to impart the chirality," Pan said. "During this process, we noticed that the sulfur atoms in the amino acids preferred to stick to the borophene more than the amino acids' nitrogen atoms did."

The researchers exposed the chiralized borophene platelets to mammalian cells in a dish and observed that their chiral shapes changed how they interacted with cell membranes and entered cells.

"This study was just the beginning. We have several projects underway to develop biosensors, drug delivery systems and imaging applications for borophene."

According to Pan, the team's findings could inform all manner of future applications, from development of higher-resolution medical imaging with contrast that could precisely track cell interactions to better drug delivery with pinpointed material-cell interactions. Understanding and controlling how the material interacts with cells could one day lead to safer, more effective implantable medical devices.

"Borophene's unique structure allows for effective magnetic and electronic control," Pan said. "This study was just the beginning. We have several projects underway to develop biosensors, drug delivery systems and imaging applications for borophene."

Borophene has applications beyond health care, with promise in sustainable energy technologies as well. Almost anywhere graphene has broken ground, expect borophene to follow.

Co-authors of the study published in ACS Nano include Parikshit Moitra, research assistant professor of nuclear engineering at Penn State and current assistant professor at the Indian Institute of Science Education and Research, and Maha Alafeef, research scientist at Penn State during the study and current assistant professor at Jordan University of Science and Technology. The Centers for Disease Control and Prevention, the U.S. National Science Foundation and the Department of Defense partially supported this research.