Electrochemical immunosensor for aflatoxin B1 (AFB1) is described that uses a composite prepared from graphene quantum dots (GQDs) and gold nanoparticles (Au NPs). The GQD-AuNP conjugate was obtained by using 2-aminothiophenol (ATP) as a linker where the carboxy groups of GQD bind to the amino groups of crosslinker via conjugation of thiol binding to the AuNP. To evaluate the conjugation of the GQD-AuNP composite, Fourier transform infrared spectroscopy (FT-IR), and transmission electron microscopy (TEM) was applied. The composite was placed on an indium tin oxide (ITO) electrode and then modified with an antibody against AFB1. By using hexacyanoferrate as the electrochemical probe, the sensor works in the 0.1 to 3.0 ng mL AFB1 concentration range, is highly specific, has good reproducibility and acceptable stability. The biosensor was applied to the analysis of (spiked) maize samples. Conceivably, the method can be utilized to sense other mycotoxins by using their respective antibodies. Graphical abstract Schematic presentation of electrochemical immunosensor for Aflatoxin B1 (AFB1) detection developed by antibodies of AFB1 (anti-AFB1) immobilization on graphene quantum dots (GQDs)-gold nanoparticles (AuNPs) composite deposited by electrophoretic deposition technique on an Indium tin oxide (ITO) surface.