For sandwich-type voltammetric immunosensor, immunoprobe contains redox species, antibody (as recognition element) and protein (as blocking agent). These proteins on the immunoprobe possess poor conductivity, which is not benefit to the improvement of current response. Herein, a novel way that the redox species was fixed on the substrate was proposed to solve this issue. Redox species (methylene blue) and hemin (a catalyst for H₂O₂) were immobilized on the substrate. Non-conductive CaCO₃ nanoparticles were used to construct the immunoprobe (glucose oxidase as blocking agent), which was regarded as impedance enhancer to hinder the electron transfer for current change (ΔI₁). In addition, when immunosensor was immersed in the glucose solution, methylene blue can be degraded by the synergism of glucose oxidase and hemin, which further increased current change (ΔI₂). The total current change (ΔI) of this immunosensor was the sum of ΔI₁ and ΔI₂. Under optimum conditions, the developed immunosensor was able to determine carbohydrate antigen 199 with good selectivity, high sensitivity and reproducibility.