Effect of control mode on the sensitivity of a microbial fuel cell biosensor with Shewanella loihica PV-4 and the underlying bioelectrochemical mechanism

A relatively poor sensitivity is a critical challenge for the application of microbial fuel cell biosensors (MFC-biosensors). This study investigated the effects of two control modes on sensor sensitivity and revealed the underlying bioelectrochemical mechanism. The results demonstrated that the sensitivity of an S. loihica PV-4 MFC-biosensor increased by 6.1 times when the anode was controlled at a constant potential (CP) instead of being operated with a fixed external resistance (ER). This obvious difference in sensor sensitivity was partly attributed to the masking effect of the observable offset current under ER mode and the lower electricity production capacity under CP mode. Moreover, the analysis of metabolic structure showed that under CP mode the anodic biofilm presented lower viability after toxic shock, due to a poorer ability to synthesize and secrete extracellular polymeric substances. Electrochemical measurements further revealed a lower capacitance under CP mode, which favored the permeation of Cd ²⁺ into the biofilm.