Researchers coat linen thread with nanotubes to make thread-based transistors

In a study published in ACS Applied Materials and Interfaces, researchers from Tufts University say they have devised the first thread-based transistors (TBTs) which can be fashioned into simple, all-thread based logic circuits and integrated circuits.

The Tufts devices work in a way that is analogous to an FET. Making a TBT involves coating a linen thread with carbon nanotubes. This creates a semiconductor surface through which electrons can travel. Attached to the thread are two thin gold wires — the source and the drain. (In some configurations, the electrons can flow in the other direction.) A third wire, the gate, is attached to material surrounding the thread such that small changes in voltage through the gate wire allows a large current to flow through the thread between the source and drain.

A critical innovation in this study is the use of an electrolyte-infused gel as the material surrounding the thread and connected to the gate wire. In this case, the gel is made up of silica nanoparticles that self-assemble into a network structure. The electrolyte gel (or ionogel) can be easily deposited onto the thread by dip coating or rapid swabbing. In contrast to the solid-state oxides or polymers used as gate material in classical FETs, the ionogel is resilient under stretching or flexing.

Compared to electronics based on polymers and other flexible materials, thread-based electronics have better flexibility, material diversity, and the ability to be manufactured without the need for cleanrooms, the researchers say. The thread-based electronics can include diagnostic devices that are extremely thin, soft and flexible enough to integrate seamlessly with the biological tissues that they are measuring.

The Tufts engineers previously developed a suite of thread-based temperature, glucose, strain, and optical sensors, as well as microfluidic threads that can draw in samples from, or dispense drugs to, the surrounding tissue. The thread-based transistors developed in this study allow the creation of logic circuits that control the behavior and response of those components. The authors created a simple small-scale multiplexer (MUX) and connected it to a thread-based sensor array capable of detecting sodium and ammonium ions — important biomarkers for cardiovascular health, liver and kidney function.

“In laboratory experiments, we were able to show how our device could monitor changes in sodium and ammonium concentrations at multiple locations,” said Rachel Owyeung, a graduate student at Tufts University School of Engineering and first author of the study. “Theoretically, we could scale up the integrated circuit we made from the TBTs to attach a large array of sensors tracking many biomarkers, at many different locations using one device.”

Said Sameer Sonkusale, professor of electrical and computer engineering at Tufts University School of Engineering and corresponding author of the study, “There are many medical applications in which real-time measurement of biomarkers can be important for treating disease and monitoring the health of patients. The ability to fully integrate a soft and pliable diagnostic monitoring device that the patient hardly notices could be quite powerful.”