An enzyme-based wearable lactate sensor incorporating complementary organic field effect transistors 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, wearable sensors. They take advantage of inducing drain current change in OFET from enzymatic reaction, however, the 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 that incorporates complementary OFETs for lactate detection with high sensitivity. In the device structure of transducer circuit, a bottom-gate p-type OFET is vertically integrated on a top-gate n-type OFET, and complementary inverter is implemented to convert the current signal to a voltage output for simple design of readout circuit with high sensitivity.1) 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.2) 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 output signal from the detection of lactate levels using the proposed device is expressed in voltages which is more stable than current signals and sensitivity is higher compared with that of single OFET-based sensors because the voltage shift induced from enzymatic reaction is amplified by the gain of the inverter. Enzyme-functionalized lactate sensor is also optimized to be the most sensitive at the concentration range of ~5 mM to 100 mM, which makes the sensor most suitable for sensing of lactate levels of human sweat (20 mM to 60 mM).3) The sensor is fabricated on a flexible substrate for conformal contact with human skin. It is expected that the proposed sensor shows the possibility of a low cost, wearable sensor