Linear alkylbenzene sulfonate (LAS), one of the most widely used synthetic surfactants in laundry detergent industry, is considered a hazardous contaminant in wastewater. In the present study, a microbial fuel cell (MFC) based biosensor is developed to quantitively determine the LAS concentration in wastewater. To do so, the developed MFC is fed with LAS concentration of 60 mg l⁻¹. Finally, a sustained biofilm is formed after almost 34 days and the highest open circuit potential of 425 mV is recorded. The maximum power and current densities of 75 mW m^-3 and 663 mA m^-3 are obtained, respectively; and the internal resistance of the MFC-based biosensor is calculated to be about 1 kΩ. After 98 hours, LAS removal and coulombic efficiency are 90% and 65%, respectively. A linear correlation between the current density and LAS concentration (in the range of 10-120 mg l^-1) is obtained. Furthermore, a comprehensive model is used to interpret the output electrical signal of the MFC representing temporal and spatial distributions of different microorganisms as well as the hierarchal processes of the LAS biodegradation. The competition between electrogens and methanogens in the biofilm; and also, the effect of external resistance on electrogen concentration are shown as well. Besides, the MFC-based biosensor desirably performed as a power generator and purifier in addition to being an accurate biosensor.