Real‐Time Multi‐Ion Detection in the Sweat Concentration Range Enabled by Flexible, Printed, and Microfluidics‐Integrated Organic Transistor Arrays

Abstract Organic electrochemical transistors (OECTs) show remarkable promise as biosensors, thanks to their high signal amplification, simple architecture, and the intrinsic flexibility of the organic material. Despite these properties, their use for real‐time sensing in complex biological fluids, such as human sweat, is strongly limited due to the lack of cross‐sensitivity and selectivity studies and the use of rigid and bulky device configurations. Here, the development of a novel flexible microfluidics‐integrated platform with an array of printed ion‐selective OECTs enables multi‐ion detection in a wearable fashion. This is achieved by coating the poly(3,4‐ethylene dioxythiophene):polystyrene sulfonate (PEDOT:PSS) channels of the transistors with three different ion‐selective membranes (ISMs). Systematic electrical and sensing analysis of the OECTs with ISMs show a minimal impact of the membranes on the electrical and time responses of the transistors while providing high ion selectivity. This work combines for the first time real‐time and selective multi‐ion detection with an array of inkjet‐printed and flexible organic transistors coated with different ISMs, demonstrating state‐of‐the‐art sensing capabilities of ≈10 µA dec⁻¹ for potassium, sodium, and pH. This flexible OECTs sensing platform paves the way to the next generation devices for continuous electrolytes monitoring in body fluids.