Revolutionary Transistor Could Allow Wearable Devices to Measure Sodium and Potassium in Blood

The electrochemical transistor is compatible with blood and water and can amplify important signals, paving the way for its application in biomedical sensing. The transistor could allow for the use of wearable devices for onsite signal processing, right at the biology-device interface. Some of its likely applications could be for measuring heartbeat and the levels of sodium and potassium in blood, as well as eye motion in studies of sleep disorders.

The vertical electrochemical transistor developed by a transdisciplinary research team at Northwestern University (Evanston, IL, USA) is based on a new kind of electronic polymer and a vertical, instead of planar, architecture. The transistor conducts electricity as well as ions, and is stable in air. The design and synthesis of the new materials, and the fabrication and characterization of the transistor was made possible by the collaborative expertise of chemists, materials scientists and biomedical engineers in the research team.

In order to make electronic circuits more reliable and powerful, there is a need for two types of transistors: p-type transistors that carry positive charges and n-type transistors that carry negative charges. These types of circuits are called complementary circuits. In the past, researchers have faced a challenge in building n-type transistors which are also typically unstable. The work by the transdisciplinary research team is the first to demonstrate electrochemical transistors with similar and very high performance for both types (p+n) of electrochemical transistors. This helped the researchers fabricate highly efficient electrochemical complementary circuits.

“All modern electronics use transistors, which rapidly turn current on and off,” said Tobin J. Marks, a co-corresponding author of the study. “Here we use chemistry to enhance the switching. Our electrochemical transistor takes performance to a totally new level. You have all the properties of a conventional transistor but far higher transconductance (a measure of the amplification it can deliver), ultra-stable cycling of the switching properties, a small footprint that can enable high density integration, and easy, low-cost fabrication.”

“This exciting new type of transistor allows us to speak the language of both biological systems, which often communicate via ionic signaling, and electronic systems, which communicate with electrons,” said Jonathan Rivnay, professor of biomedical engineering at the McCormick School. “The ability of the transistors to work very efficiently as ‘mixed conductors’ makes them attractive for bioelectronic diagnostics and therapies.”

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