Oxygen availability is a potential rate-limiting step in the bioelectrochemical process catalyzed by microbes in microbial fuel cells (MFC). Determination of oxygen availability using a minimally invasive oxygen sensor is advantageous in terms of ease of usage, maintenance and cost-effectiveness as compared to using conventional probe-type oxygen sensors. The utility of this method is substantiated by using this sensor to demonstrate the relationship between oxygen availability and current density. 10 % drop in oxygen concentration resulted in a concomitant drop in current density by about 36 %, further establishing the criticality of monitoring oxygen levels in the MFC. The detachable sensor membrane of the minimally invasive sensor confers multiple advantages. The novel method would enable real-time monitoring of oxygen in MFCs, simplify process optimization and validation and more importantly, provide an impetus for development of more efficient MFC designs.