Real-time bioelectronic sensors based on electroactive bacteria with organic electrochemical transistors

Whole-cell microbial biosensors with electrogenic bacteria are emerging electrochemical devices that can perform complex functions, operate in challenging environments, and send and receive information electrochemically. Recent work has explored interfacing electrogenic bacteria with organic electrochemical transistors (OECTs) to produce compact electrochemical devices that can amplify extracellular electron transfer and respond more quickly than conventional devices. However, this work has focused primarily on the steady-state current produced. Understanding the dynamic sensor response to changing environmental conditions is important for utilizing microbial OECTs as real-time biosensors. Here, we study the dynamic response of OECTs interfaced with the electrogenic bacterium Shewanella oneidensis MR-1 and find that the source-drain current exhibits a first-order dynamic response to a step change in lactate concentration. By calibrating the living bioelectronic devices over a wide range of concentrations, the devices can be used as biosensors to monitor changes in lactate concentration in the solution based on the rate of change in current. We also show that the sensitivity and range of the device can be tuned through variations of the source-drain voltage, and by increasing the source-drain voltage, we demonstrate microbial devices that can detect lactate concentrations as low as 10^-9 M. Finally, we implement microbial OECTs as compact, portable devices capable of quickly estimating chemical oxygen demand (COD) in wastewater and demonstrate a bacterial encapsulation strategy that enables reusable devices that operate in ambient conditions. This work advances the development of microbial sensors and provides a straightforward and easily implemented model for understanding the dynamic response of microbial bioelectronic sensors.