Continuous electrochemical monitoring of L-glutamine using redox-probe-modified L-glutamine-binding protein based on intermittent pulse amperometry

Abstract The development of a continuous electrochemical monitoring system using a periplasmic binding protein (PBP), which changes its conformational dynamics upon ligand binding, is promising for in situ, real-time, continuous measurement technologies for use in effective biological production processes. This study focuses on a continuous L -glutamine biosensor based on　Escherichia coli-derived L -glutamine-binding protein (QBP), a PBP that can speficically bind to L -glutamine. In this sensor, QBP was modified with a redox probe, amine-reactive phenazine ethosulfate (PES), and the conformational change in QBP through the recognition of L -glutamine was monitored electrochemically by intermittent pulse amperometry (IPA) based on the change in the access of QBP-modified PES to the electrode. This sensor exhibited a change in the current against logarithmic L -glutamine concentrations between 0.2–50 μM. Continuous monitoring of L -glutamine, based on IPA measurements, revealed that continuous changes in L -glutamine concentration were observed for both increasing and decreasing concentrations. During continuous monitoring, L -glutamine concentration was monitored between 50 and 500 μM, with a limit of detection of 50 μM. This result is expected to address the future development of an electrochemical biosensor for in situ, real-time, continuous monitoring of various metabolites based on PBPs.