<p>Carbohydrate antigen 19–9 (CA19 - 9) can be used as a biomarker for pancreatic cancer. Measuring the concentration of CA19 - 9 in serum is essential for screening pancreatic cancer patients. In this paper, a dual-electric signal outputs biosensor based on ping pong chrysanthemum-like Bi-BiOI and ternary core–shell structured Pd@AuPt was constructed for ultra-sensitive detection of tumor marker CA19 - 9 using differential pulse voltammetry (DPV) and chronoamperometry (i-t). Ping pong Chrysanthemum-like Bi-BIOI was prepared via one-pot hydrothermal method. To realize the covalent bonding of bismuth-based materials with MWCNT, bismuth-based materials were functionalized by amino groups. MWCNT-NH₂-Bi-BIOI with large specific surface area and remarkable electrical conductivity was used as the sensing platform. Ternary core–shell structured Pd@AuPt with peroxide-like activity and enhanced biocompatibility immobilized massive antibodies through covalent Au–N and Pt–N bonds, thus broadening the linear range of the immunosensor. Based on the above materials, a dual-electric signal outputs biosensor was constructed for detecting CA19 - 9. Under optimal conditions, the detection range of DPV and i-t is 0.001–150 U/mL, the detection limit of DPV is 0.0003 U/mL, and that of i-t is 0.00024 U/mL. In addition, the dual-electric signal outputs immunoassay excels in anti-interference, splendid reproducibility and high recovery in actual sample detection, indicating that the immunosensor is a promising approach to be applied to&#xa0;the detection of CA19 - 9 in clinical diagnosis.</p> Graphical abstract <p></p>