Aflatoxin B1(AFB1),an aflatoxin is extremely toxic among mycotoxins in contaminated food products butit is very difficult to be quantitatively detected by existing methods.Impedimetric immunosensor is an advantageously label-free and fast assay.Nevertheless,its applications are limited by low sensitivity when the target molecule is small such as AFB1 due to relatively low impedance change during detection.Herein for the first time reduced graphene oxide(rGO)is nanocomposed with polypyrrole(PPy)and pyrrolepropylic acid(PPa)as a unique sensing platform,in which rGO greatly improves the conductivity and stability,PPa provides covalent linkers for probe immobilization and PPy endows the filmelectroactivity from its inherent electrochemical doping/dedoping property for impedance measurements,thus significantly improving the sensitivity to detect AFB1 in a range of 10 fg mL-1 to 10 pg mL-1with high specificity and good reproducibility.This work demonstrates a novel method to sensitively detect small molecule by using immunoassay.