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For many years, tracking the electrical activity within living cells has relied heavily on the use of electrodes and dyes. However, recent advancements by engineers at the University of California San Diego suggest a revolutionary approach: utilizing quantum materials that are only a single atom thick to accomplish this task using light alone.
A study published on March 3 in Nature Photonics highlights how these ultra-thin semiconductors, which confine electrons to two-dimensional spaces, can effectively sense the biological electrical activity of living cells at high speed and resolution.
Researchers have long aimed to improve the methods for monitoring the electrical signals of the body’s most active cells, including neurons, cardiac muscle cells, and pancreatic cells. These small electrical impulses are crucial for functions ranging from thought processes to movement and metabolism. Yet capturing them in real-time and across large areas has proved difficult.
Traditional electrophysiology can provide precise data through invasive microelectrodes, but it faces scalability challenges. The implantation of electrodes across extensive tissue areas often leads to considerable damage, and even sophisticated probes usually record only a few hundred channels simultaneously. In contrast, optical methods such as calcium imaging monitor larger populations of cells but do so indirectly, tracking secondary changes that may not accurately represent the actual electrical activity happening in the cells.
The engineers from UC San Diego have introduced a novel strategy to address these limitations: a rapid, all-optical technique for detecting voltage fluctuations using atom-thick semiconductors. This breakthrough stems from the interaction of the materials’ electrons with light; under the influence of an electric field, these electrons toggle between two states—excitons (electron-hole pairs lacking charge) and trions (charged excitons). The research team discovered that this transition from excitons to trions in monolayer semiconductors can effectively detect electrical signals from heart muscle cells without needing invasive electrodes or voltage-sensitive dyes that could disrupt cellular activity.
Essentially, the quantum characteristics of the material serve as the sensor itself.
“We believe that the voltage sensitivity of excitons in monolayer semiconductors has the potential to enable high spatiotemporal investigation of the brain’s circuitry,” stated Ertugrul Cubukcu, the lead author of the study and a professor in both the Aiiso Yufeng Li Family Department of Chemical and Nano Engineering and the Department of Electrical and Computer Engineering at the UC San Diego Jacobs School of Engineering.
Cubukcu and his team focused their research on the quantum properties of monolayer molybdenum sulfide. They noted not only its biocompatibility but also an advantageous feature: during its production, this semiconductor naturally develops sulfur vacancies, resulting in a high density of trions. This intrinsic defect enhances its sensitivity to fluctuations in nearby electric fields produced by living cells, facilitating the spontaneous conversion from excitons to trions.
By monitoring variations in the material’s photoluminescence, the researchers were able to map the electrical activity of cardiac muscle cells in real time, achieving speeds that surpass any existing imaging technologies, as emphasized by the team.
The implications of this technology are vast. It holds the potential to enable scientists to map dysfunctions within large networks of excitable tissue, exploring areas from the surface to deeper layers. This could deepen understanding of the mechanisms behind various neurological and cardiac diseases, leading to improved insights into how these conditions disrupt the body’s electrical systems. Additionally, it may enhance therapeutic approaches involving electrical neuromodulation—such as deep brain stimulation for Parkinson’s disease or cardiac pacing for arrhythmias. Furthermore, this research could pave the way for discovering new quantum materials that facilitate a non-invasive, high-speed method for probing the electrical activity in living organisms.
This study received funding from several prestigious institutions, including the National Science Foundation and the National Institutes of Health, among others. Device fabrication was carried out at the San Diego Nanotechnology Infrastructure at UC San Diego, a member of the National Nanotechnology Coordinated Infrastructure, supported by the National Science Foundation.
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