Graphene “camera” images the activity of living heart cells

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Scientists can make these measurements with microelectrode arrays (networks of tiny tubes) inserted into the cell membrane. But this method is limited. Researchers can only determine the voltage in the specific cell where the electrode has been inserted.

“Recording the voltage at a point—such as in the brain—is a bit like watching a movie by looking at a pixel on a computer screen. You can know when things happen, but you can’t see the plot, you can’t see the difference in space The relevance of information,” Cohen said. The new graphene device produces a more complete image because it records the voltage at each point where the tissue is in contact with carbon atoms.

“By using our graphene device, we were able to image the entire surface at the same time,” said Halleh Balch, the lead author of the study, who was a doctoral student at Berkeley during the experiment. (She is currently a postdoctoral researcher at Stanford University.) This part is the result of the unique properties of graphene. “Graphene is atomically thin, which makes it extremely sensitive to the local environment, because basically every part of its surface is an interface,” she said. Graphene also has good electrical conductivity and is quite tough, which makes it a long-standing experimental darling of quantum physicists and materials scientists.

But in the field of biosensing, it is more like a newcomer. “The method itself is very interesting. In the sense of using graphene, it is very novel,” said Gunther Zeck, a physicist at the Vienna University of Technology, who was not involved in the research. He has studied microelectrodes in the past, and he suspects that graphene-based devices may become their true competitors in the future. Zeck said that making large microelectrode arrays can be very complicated and costly, but making large sheets of graphene may be more practical. The new device is about 1 square centimeter, but graphene sheets thousands of times larger are already on the market. By using them to create “cameras”, scientists can track the electrical impulses of larger organs.

For more than a decade, physicists have known that graphene is sensitive to voltage and electric field. But combining this insight with the chaotic reality of biological systems presents design challenges. For example, because the team did not insert graphene into cells, they had to amplify the influence of the cell’s electric field on graphene before recording.

The team used their knowledge of nanophotonics-a technique that uses light on the nanoscale-to convert the slight changes in graphene reflectance into detailed pictures of the electrical activity of the heart. They layered graphene on top of a waveguide, which is a glass prism coated with silicon and tantalum oxide, creating a tortuous path for light. Once the light hits the graphene, it enters the waveguide, then bounces it back to the graphene, and so on. “This enhances our sensitivity because you cross the graphene surface multiple times,” said research co-author Jason Horng, a laboratory partner during Dr. Balch’s period. “If there is some change in the reflectance of graphene, then this change will be amplified.” This magnification means that small changes in the reflectance of graphene can be detected.

The team also managed to capture the mechanical movement of the entire heart-the contraction of all cells at the beginning of the heartbeat and subsequent relaxation. As the heart cells beat, they are dragged onto the graphene sheet. This causes the light leaving the graphene surface to be slightly refracted, and the electric field of the cell has changed its reflectivity. This led to an interesting observation: When the researchers used a muscle inhibitor drug called blebbistatin to stop the cells from moving, their light-based records showed that the heart had stopped, but the voltage was still spreading through its cells.

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