Here we prepared an electrochemical immunosensor employing Au sheet as working electrode, Fe3O4 magnetic nanoparticles (MNPs) as supporting matrix and hemin/G-quadruplex DNAzyme as signal amplifier for determination of hepatitis B virus surface antigen (HBsAg). First, the primary antibody of HBs (Ab1) was immobilized on the surface of the carboxyl-modified MNPs. Then, the assembly of antibody and alkylthiol/Gquadruplex DNA/hemin on gold nanoparticles was used as bio-bar-coded nanoparticle probe. Protein target was sandwiched between the primary antibody of HBs (Ab1) immobilized on the MNPs and hemin bio-barcoded AuNPs probe labeled antibody (Ab2). Hemin/G-quadruplex structure as HRP mimicking-DNAzyme significantly improved the catalytic reduction of H2O2 by oxidation of methylene blue (MB). Square wave voltammetry signals of MB provided quantitative measurements of HBsAg with a linear concentration range of 0.3–1000 pgmL−1 and detection limit of 0.19 pgmL−1. Due to efficient catalytic activity of HRP mimicking- DNAzyme, the proposed immunosensor exhibited high sensitivity and it holds great promise for clinical application and provides a new platform for immunosensor development and fast disease diagnosis.
