FePO4 is biocompatible and can act as a kind of promising enzyme mimetic. Unfortunately, the electrical conductivity of FePO4 is poor. In order to enhance its conductivity, FePO4 was embedded into nanofibers consisting of amorphous carbon and reduced graphene oxide (rGO) by an electrospinning technique. As a sensing material for monitoring superoxide anion (O-2(center dot-)) and typically operated at 0.5 V (vs. SCE), it displays high sensitivity (9.6 mu A center dot mu M-1 center dot cm(-2)), a low detection limit (9.7 nM at S/N = 3), a wide linear response range (10 nM to 10 mu M), and fast response (1.6 s). Due to its low detection limit and fast response, the sensor in our perception has a large potential for detecting superoxide anions released by HeLa cancer cells.