Cascade signal amplifying strategy for ultrasensitive detection of tumor biomarker by DNAzyme cleaving mediated HCR

Tumor biomarkers are a kind of important biomolecules for aiding cancer diagnosis and assessing tumor efficacy, among which alpha-fetoprotein (AFP) is a crucial tumor biomarker for the early diagnosis of hepatocellular carcinoma. In this study, a novel cascade signal amplifying strategy was designed for the ultrasensitive detection of AFP by DNAzyme cleaving-mediated hybridization chain reaction (HCR). The primary antibody was immobilized on the Au nanoparticles modified glassy carbon electrode, which subsequently captured AFP and the secondary antibody. Then, streptavidin was combined with the biotin-modified secondary antibody and Cu2+-specific DNAzyme. When Cu2+ was present, the substrate strand of the DNAzyme would cleave and produce an ssDNA end. Finally, HCR was triggered to form long double-stranded DNA on the electrode, which would greatly inhibit the charge transfer at the electrode/solution interface. Therefore, the DNAzyme cleaving-mediated HCR strategy can be applied as cascade signal amplification for the ultrasensitive electrochemical determination of tumor biomarker AFP. Under optimal conditions, the immunosensor exhibits a broad linear range of 0.001−100 ng·mL−1 (R2 = 0.990) and a low detection limit of 15.8 fg·mL−1. The proposed sensor displays high sensitivity and selectivity for AFP detection, which can be employed as a universal sensing platform in clinical diagnostics.