ABSTRACTUsing microbial fuel cells (MFCs) as biosensors ensures a sustainable method for water quality detection. However, the research on MFC‐based biosensors with a tubular setup is still scarce. In this study, a tubular multi‐array MFC‐based biosensor setup with air‐cathodes was assembled under the membrane electrode assembly configuration. Three different materials, including carbon black (CB), Pt/C (PtC), and polyaniline (PANI), were synthesized and coated on the membrane‐facing side of the air‐cathode to demonstrate the effects of modified air‐cathodes on the overall performance of the MFC‐biosensors. Unmodified carbon cloths were used as anodes. Three days of startup period were required by the biosensors before producing an electrical signal output. The highest current density was obtained by the polytetrafluoroethylene (PTFE)/CB/PtC (0.31 A m−2) sample followed by PTFE/CB/PANI (0.09 A m−2), and lastly PTFE/CB (0.05 A m−2). The control (PTFE only) sample did not generate any noticeable electrical signal. The electrochemical impedance spectroscopy analysis showed that the incorporation of PtC on the PTFE/CB sample lowered the charge transfer resistance (Rct), whereas the addition of PANI increased the Rct. Despite the differences in Rct values, both PTFE/CB/PtC and PTFE/CB/PANI samples demonstrated a better current density production than the PTFE/CB sample. Thus, modified air‐cathodes further elevated the biosensor's performance.