Fabrication of cylindrical diffusion-facilitated organic electrochemical transistor and its sweat glucose sensing application

Organic electrochemical transistors (OECTs) have been widely tested used for biosensing applications due to high sensitivity, low operating potential, better signal-to-noise ratio and operation in aqueous medium. The electrochemical de-doping in OECTs is a diffusion-controlled process which crucially depends on the geometry of the channel. This report presents OECT with cylindrical channel and its application in detection of sweat glucose concentration. The cylindrical channel OECTs were fabricated by incorporating PEDOT:PSS-coated single cotton fibre as a channel. The cylindrical diffusion of ions into the channel is confirmed by the parallel combination of a resistor and Warburg impedance in electrochemical impedance spectroscopy. The non-linear current–voltage characteristics of the device closely follow Bernard-Malliaras model. The transconductance has been derived to be 2.48 × 10⁻⁴ S from the transfer characteristics. The developed OECTs were deployed for glucose sensing by bioconjugating the gate terminal with glucose oxidase enzyme. A 1.4 mg/dL limit of detection, 2.8 mg/dL limit of quantification and 7.14-s average response time have been achieved with the device. As the device shows higher responsivity between 5 and 50 mg/dL, the OECT has been demonstrated as a wearable sweat glucose sensor.