Microfabricated Ion‐Selective Transistors with Fast and Super‐Nernstian Response

TLDR

Transistor‑based ion sensors have advanced, yet the reliance on a liquid electrolyte reservoir between the ion‑selective membrane and channel hampers miniaturization, resulting in bulky, mechanically inflexible devices that limit high‑performance wearable and implantable sensor development. The study demonstrates microfabricated ion‑selective organic electrochemical transistors that replace the liquid reservoir with a thin polyelectrolyte film containing mobile sodium ions. The OECTs achieve 4 mS transconductance by employing this thin polyelectrolyte film as the internal reservoir. The devices exhibit selective ion detection with a ~1 s response, super‑Nernstian sensitivity of 85 mV dec⁻¹, high current sensitivity of 224 µA dec⁻¹, and maintain reproducible performance after five months, positioning them for implantable and wearable electronics.

Abstract

Transistor-based ion sensors have evolved significantly, but the best-performing ones rely on a liquid electrolyte as an internal ion reservoir between the ion-selective membrane and the channel. This liquid reservoir makes sensor miniaturization difficult and leads to devices that are bulky and have limited mechanical flexibility, which is holding back the development of high-performance wearable/implantable ion sensors. This work demonstrates microfabricated ion-selective organic electrochemical transistors (OECTs) with a transconductance of 4 mS, in which a thin polyelectrolyte film with mobile sodium ions replaces the liquid reservoir. These devices are capable of selective detection of various ions with a fast response time (≈1 s), a super-Nernstian sensitivity (85 mV dec-1 ), and a high current sensitivity (224 µA dec-1 ), comparing favorably to other ion sensors based on traditional and emerging materials. Furthermore, the ion-selective OECTs are stable with highly reproducible sensitivity even after 5 months. These characteristics pave the way for new applications in implantable and wearable electronics.