Signal Amplification of Electrochemical ELISA for the Detection of Alpha-Fetoprotein Using Core-Shell Fe3O4@Au Nanoparticles as Labels

A novel electrochemical enzyme-linked immunosorbent assay (ELISA) system of o-phenylenediamine (OPD)-H2O2-horseradish peroxidase (HRP) for sensitive detection of alpha-fetoprotein (AFP) was designed using magnetic core-shell Fe3O4@Au nanoparticles as labels. The detection antibodies were prepared by immobilization of HRP-anti-AFP and HRP onto the surface of Fe3O4@Au nanoparticles (Fe3O4@Au-HRP-anti-AFP). After the sandwich-type immunoreaction on polystyrene 96-well microtiter plate, the formed HRP-labeled immunoconjugate showed good enzymatic activity for the oxidation of OPD by H2O2. Enhanced detection sensitivity was achieved where the large surface area of Fe3O4@Au nanoparticles carriers increased the amount of HRP on per sandwich-type immunoreaction. The approach provided a linear response range between 0.01 and 200 ng . mL(-1) with a detection limit of 5 pg . mL(-1) The proposed electrochemical ELISA method exhibited good precision, high sensitivity and acceptable reproducibility, and could be further developed for clinical detections of AFP and other biomarkers.