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A nonenzymatic sandwich-type electrochemical immunosensor was developed by means of a modified glassy carbon electrode: GCE/chitosan/Au nanoparticle (AuNP)/anti-Aflatoxin B₁ (a AFB₁), and a Fe₃O₄ magnetic core with a gold shell functionalized with 3-((2-mercaptoethylimino)methyl)benzene-1,2-diol and labeled with an AFB₁. The immunosensor was used for the detection of Aflatoxin B₁ as a model antigen. The current originated from the conversion of catechol to o-quinone and vice versa within a quasi-reversible two electrons–two protons reaction, considered as the response. The electrochemical studies demonstrated that the proposed immunoelectrode can be used to detect AFB₁ in the range of 0.6–110ngmL⁻¹ with a detection limit of 0.2ngmL⁻¹. This immunosensor can be simply regenerated by using an external magnetic field which ensures a reproducible response.