May 4 2017
Changes in photocurrent before and after exposure to UV light. Persistent photoconductivity is demonstrated even hours after the UV light has been turned off. This is illustrated by the pictograms showing charge carriers that come into contact with cells at the interface during in vitro experiments. (credit: NC State University)
A team of researchers at North Carolina State University have created a new approach for controlling the behavior of cells on semiconductor materials, using light to change the conductivity of the material itself.
There’s a great deal of interest in being able to control cell behavior in relation to semiconductors – that’s the underlying idea behind bioelectronics. Our work here effectively adds another tool to the toolbox for the development of new bioelectronic devices.
Albena Ivanisevic,Professor of Materials Science and Engineering, NC State
The new method makes use of a phenomenon referred to as persistent photoconductivity. Materials that display persistent photoconductivity become a lot more conductive when light is shone on them. When the light is taken away, it takes the material a long time to return to its original conductivity.
When conductivity is raised, the charge at the surface of the material surges. And that increased surface charge can be used to direct cells to stick to the surface.
This is only one way to control the adhesion of cells to the surface of a material. But it can be used in conjunction with others, such as engineering the roughness of the material’s surface or chemically modifying the material.
Albena Ivanisevic,Professor of Materials Science and Engineering, NC State
For this research, the team showed that all three characteristics can be used together, working with a gallium nitride substrate and PC12 cells – a series of model cells used extensively in bioelectronics testing.
The researchers analyzed two groups of gallium nitride substrates that were identical; with the only exception that one group was exposed to UV light – activating its persistent photoconductivity properties – while the second group was not.
There was a clear, quantitative difference between the two groups – more cells adhered to the materials that had been exposed to light. This is a proof-of-concept paper. We now need to explore how to engineer the topography and thickness of the semiconductor material in order to influence the persistent photoconductivity and roughness of the material. Ultimately, we want to provide better control of cell adhesion and behavior.
Albena Ivanisevic,Professor of Materials Science and Engineering, NC State
The paper, “Persistent Photoconductivity, Nanoscale Topography and Chemical Functionalization Can Collectively Influence the Behavior of PC12 Cells on Wide Band Gap Semiconductor Surfaces,” is published in the journal Small. The paper’s lead author is Patrick Snyder, a Ph.D. student in Ivanisevic’s lab. The paper was co-authored by Ronny Kirste of Adroit Materials, and Ramon Collazo, an assistant professor of materials science and engineering at NC State.
The research was conducted with support from the U.S. Army Research Office, under grant number W911NF-15-1-0375, and the National Science Foundation, under grant number DMR-1312582.