Persistent photoconductivity used to stimulate neurotypic cells

A material that demonstrates persistent photoconductivity gains a negative charge on its surface when exposed to the right wavelength of light, and retains that charge even after the light is removed. The correct wavelength of light, and how long the material retains its charge, varies from material to material.

Researchers have known for years that electric charge can stimulate a cell, but existing technologies for conducting related experiments are often invasive or require specialized equipment. They can also be extremely time consuming.

"We wanted to take advantage of the electronic properties of the semiconductor gallium nitride, which is biocompatible, making it a true bioelectronic interface," says Patrick Snyder, a Ph.D. student at North Carolina State University and lead author of a paper on the work. "The result is a faster, noninvasive way to stimulate cells that doesn't require specialized equipment."

Specifically, the researchers exposed a gallium nitride substrate to ultraviolet (UV) light, creating a negative charge on its surface. As soon as the UV light was removed, researchers poured a solution containing PC12 neurotypic cells into the container with the substrate. The researchers then introduced a dye that allowed them to measure calcium levels in the PC12 cells.

What the researchers found was that PC12 cells were stimulated when they came into contact with the charged gallium nitride substrate, as evidenced by increased calcium ion levels within the cells, when compared to a control group that did not come into contact with a charged substrate.

This is evidence of altered behavior because ions are important in neurotypic cell activity. For example, calcium ions play key roles in neuronal signaling.

"In addition to advancing our fundamental understanding of what this material is capable of, we're optimistic that it can facilitate work by many labs interested in advancing research on cellular behavior," says Albena Ivanisevic, a professor of materials science and engineering at NC State and corresponding author of the paper.

The paper, "Non-Invasive Stimulation of Neurotypic Cells Using Persistent Photoconductivity of Gallium Nitride," is published in the open-access journal ACS Omega. The paper was co-authored by Ramon Collazo, an assistant professor of materials science and engineering at NC State; Pramod Reddy, a postdoctoral researcher at NC State and employee of Adroit Materials; Ronny Kirste of Adroit Materials; and Dennis LaJeunesse, an associate professor of nanoscience at the University of North Carolina-Greensboro.

The work was done with support from the U.S. Army Research Office, under grant W911NF-15-1-0375; and the National Science Foundation, under grants DMR-1312582 and ECCS-1653383.