Making Bioelectronics More Effective and Compact

Bioelectronic devices play a key role in medicine. Not only do they help with the health diagnostic process by sensing chemical biomarkers and brain or heart activity to measure pathology, but they also assist in treating ailments such as epilepsy, pain, diabetes, or accelerating tissue regeneration. 

Recent work from Northwestern Engineering’s Jonathan Rivnay could pave the way for bioelectronic devices that are less invasive and even more powerful for diagnosis and health monitoring.

Often, recorded signals produced by human tissues can be weak, making them more susceptible to added noise or distortion when those signals are transmitted from implanted or wearable bioelectronics. This can make it difficult for devices to properly analyze signals and perform effectively.

The work by Rivnay and his team addresses this challenge by bringing some of the function from these “back end” electronics to the actual recording site. This breakthrough may result in a higher level of amplification, and could similarly enable on signal processing, decision making, and other benefits at the interface of electronics and tissues. Further, those benefits will enable more integrated, multi-functional, and potentially power-efficient devices.

“Our polymer-based transistors can act as active recoding sites to amplify electrophysiological signals,” said Rivnay, assistant professor of biomedical engineering at the McCormick School of Engineering. “This paper demonstrates the colocalization of two different polymer transistors in an arrangement that allows for high amplification of biopotentials on a very small footprint, the size of a traditional passive recording site, or microelectrode.”

We believe this concept can be extended further, creating faster and more stable local amplification. Jonathan Rivnay Assistant Professor of Biomedical Engineering

The work was described in the paper “Ambipolar Inverters Based on Cofacial Vertical Organic Electrochemical Transistor Pairs for Biosignal Amplification,” which was published September 8 in the journal Science Advances. Reem Rashid, a biomedical engineering graduate student in Rivnay’s lab, was the first author. She spearheaded the effort, including coordinating with synthetic chemistry collaborators from the University of Oxford.

In this work, Rivnay and his collaborators flipped polymer transistors on their side, making vertical transistors, and tested simple complementary circuits based on these elements. They explored their performance on the benchtop, and validated that the concept could work by measuring heart activity. The team then developed the architecture that enabled these transistors to be very close to each other – to make the transistors occupy a very small space and still perform the circuit function of amplifying the biological signals.

Rivnay said that as new bioelectronic materials are developed, more advances could arrive.

“We believe this concept can be extended further, creating faster and more stable local amplification,” Rivnay said. “Further, it may allow for self-calibrating biochemical sensors — sensors that have a built-in reference at the same recording site — opening up new possibilities for multi-analyte sensing.”