Multi-amplification of the signal of voltammetric immunosensors: Highly sensitive detection of tumor marker

An immunosensor for the determination of carbohydrate antigen 199 based on calcium carbonate sphere as probe and the degradation of methylene blue by hemin as catalyst was fabricated. [Display omitted] •Degradation of signal substance and non-conductive probe were used to increase the sensitivity of voltammetric immunosensor.•Redox species was fixed on the substrate for sandwich-type immunosensor.•CaCO3 nanoparticles were used as support to construct immunoprobe. 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.