Abstract <p>In the article, polypyrrole functionalized graphene oxide (PPy/rGO) composites and gold nanoparticles (AuNPs) were prepared, and after modifying them onto a glassy carbon electrode (GCE), a biosensor was constructed for the detection of Mucin 1 (MUC1) using aptamer (Apt) as the molecular recognition original and the modified electrode as the signal conversion element, and CP–Au–Thi (CPs) were used as the probes to detect electrochemical signals, and when there was a presence of the detected substance, MUC1 in the system, it could be combined with an Apt to trigger the dissociation of CPs from the electrode surface, and the electric signal was increased. When the detector MUC1 was present in the system, it can bind to the Apt to trigger the dissociation of CPs from the electrode surface and the electrical signal increases. Cyclic voltammetry (CV), differential pulse voltammetry (DPV), and electrochemical impedance spectroscopy (EIS) were used to detect the changes in electrochemical signals. The sensor showed good linearity for the detection of MUC1 in the concentration range of 1.0&#xa0;fg&#xa0;mL⁻¹ to 10&#xa0;ng&#xa0;mL⁻¹, with a detection limit of 0.5&#xa0;fg&#xa0;mL⁻¹. The sensor showed good performance in the detection of human serum samples, and has a promising application in the detection of tumor markers.</p> Graphical abstract <p></p>