Highly sensitive impedimetric immunosensor based on single-walled carbon nanohorns as labels and bienzyme biocatalyzed precipitation as enhancer for cancer biomarker detection

• Enzymatically catalyzed precipitates based on bienzyme.
• Functionalized single-walled carbon nanohorns (SWCNHs) as molecular tags were first reported.
• A sandwich electrochemical immunosensor for AFP detection was developed.

A novel sandwich-type electrochemical immunosensor based on functionalized nanomaterial labels and bienzyme (horseradish peroxidase and glucose oxidase) biocatalyzed precipitation was developed for the detection of α-fetoprotein (AFP). The enzymes linked to functionalized nanomaterials as biocatalysts could accelerate the oxidation of 4-chloro-1-naphthol (4-CN) by H2O2 to yield the insoluble product on the electrode surface; the mass loading of the precipitates on the device led to a significant enhanced signal. Cyclic voltammetry and electrochemical impedance spectroscopy techniques were used to monitor the enhanced precipitation of 4-CN that accumulated on the electrode surface and subsequent decrement in the electrode surface area by monitoring the reduction process of the Fe(CN)64−/3− redox couple. Under optimal conditions, the proposed immunosensor showed a high sensitivity and a wide linear range from 0.001 to 60 ng mL−1 with a low detection limit of 0.33 pg mL−1. Moreover, the immunosensor exhibited good selectivity, acceptable stability and reproducibility. The amplification strategy showed good promise for clinical screening of tumor biomarkers.