A new device for investigating the internal extracellular pH dynamics in the brain

Researchers at the University of Tohoku have developed the first comprehensive miniature pH probe to real-time investigate internal extracellular pH dynamics in deep brain structures.

In our brains, over a billion dedicated workers – neurons and glial cells – form complex and efficient networks that constantly communicate with each other with subtle chemical signals to control our output behavior.

Brain chemistry is the basic language among brain cells. In our healthy brain, chemistry remains relatively neutral and must constantly regulate acid-base fluctuations; otherwise it can lead to chronic brain disorders such as mental illness, glioma and seizures. The correlation in brain pH fluctuations with brain signaling and functions, provides a clearer understanding of the influence of pH on the way our brain works and how it breaks down in a diseased state.

However, despite recent technical advances in electrical brain imaging and chemical surveillance technologies, there are still limitations in measuring chemical signaling, especially the pH of living organisms, ie. In vivo.

The research team addressed these limitations with a pioneering hybrid device that combined two different technologies: a thin-fiber strand with seamless integration of electrical and optical functions, and chemical sensors with light-defined measuring points. The combination enables in vivo spatially discernible detection of internal chemical signaling within the brain, especially deeper areas, with high spatial, temporal and chemical resolution.

We used a thermal drawing process commonly used in the telecommunications industry to produce fibers that integrate multiple functions, such as optical waveguides, electrodes, and chemical channels. “

Yuanyuan Guo, Assistant Professor, Institute for Border Research in Interdisciplinary Sciences, Tohoku University

Collaboration with Professor Tatsu Yoshinobu of the Graduate Faculty of Biomedical Engineering led to the fusion of the active component – a chemical sensor with light addressing – to the fiber to realize a hybrid probe of a hybrid sensor for in vivo detection of in vivo subtle chemical changes in the brain. The first prototype focused on pH detection.

The probe was also tested on in vivo measurements thanks to Professor Hajime Mushiake from the Faculty of Medicine. He was able to detect mild pH fluctuations in response to seizures in rats.

“The next step for our team is to improve the spatial, temporal and chemical resolution to a level that meets the criteria of internal neural dynamics,” Guo added. “Our technological discovery will advance our basic understanding of brain chemistry and its correlation with brain functions.”


Journal reference:

Guo, Y., and others. (2020) Miniature multiplexed pH probe without labels in vivo. Biosensors and bioelectronics. doi.org/10.1016/j.bios.2020.112870.