An enzyme-based wearable lactate sensor with subthreshold operation of a dual-gate organic transistor for high sensitivity

Abstract

Enzyme-based biochemical sensors based on organic thin film transistors (TFTs) have gained much attention for their potential applications as low-cost and bio-compatible wearable sensors. In such applications, the enzymatic redox reaction integrated into individual TFT induces an amplified concentration-dependent drain current. For the realization of wearable devices, however, low power consumption is essentially required and not to mention high sensitivity. In this work, we exploit subthreshold operation of an extended-gate type dual-gate TFT for lactate detection with low power and high sensitivity. In the dual-gate TFT configuration, the top gate is separated and extended from the device to serve as an extended sensing gate (ESG) on which lactate oxidase enzyme is functionalized. The enzyme-functionalized ESG composes biofuel cell with Ag/AgCl reference electrode in aqueous media. We have observed that the enzymatic redox chain reaction of lactate occurring in the biofuel cell causes potential difference between the ESG and the reference electrode, which results in threshold voltage shift in the dual-gate TFT. Moving forwards, through strategic subthreshold operation of dual-gate TFT where its subthreshold slope (SS) is higher than single-gate transistor, it enabled not only lower power consumption but also higher sensitivity in comparison to operation in single-gate transistor. The device is fabricated on a flexible substrate for a skin-like wearable sensor, illustrating its potential as a wearable biochemical sensor.