An enzyme-based lactate sensor incorporating a three-dimensional complementary inverter for high sensitivity

Abstract

Enzyme-based biochemical sensors based on organic field-effect transistor (OFET) have gained attention for their potential applications as low-cost, disposable, wearable sensors. They take advantage of inducing drain current change in OFET from enzymatic reaction, however, the induced current signal is not stable and signal-to-noise ratio is not large enough to be easily detected. In this study, we propose a new strategy of an extended-gate type inverter incorporating three-dimensional complementary organic field-effect transistors (3D-COFETs) for lactate detection with higher sensitivity. In the device structure of 3D-COFETs, a bottom-gate p-type OFET is vertically integrated on a top-gate n-type OFET with the gate shared in-between, and complementary inverter is implemented with this transistor-on-transistor structure. For lactate detection, enzyme-functionalized gold electrode is used as an extended-gate of complementary inverter, and it 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 two electrodes which results in switching voltage shift in the complementary inverter. The proposed 3D-COFETs structure itself has advantages in sensing applications within complementary integrated circuit systems thanking to its higher transistor density. The output signal from the detection of lactate levels using the proposed 3D-COFETs inverter is expressed in voltages which is more stable than current signals and sensitivity is higher compared with that of single OFET-based biochemical sensors because the voltage shift induced from enzymatic reaction is amplified by the gain of the inverter. It is expected that the proposed biochemical sensor incorporating 3D-COFETs is a promising candidate for highly sensitive biosensors in practical applications.