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Functional Magnetic Nanoparticles for Clinical Application: Electrochemical Immunoassay of Hepatitis B Surface Antigen and α-Fetoprotein

This work reports an efficient method to quantify the Hepatitis B surface antigen and α-fetoprotein in human serum using a functional magnetic nanoparticle-assisted sandwich-type electrochemical immunoassay. The Fe 3 O 4 magnetic nanoparticles were first modified with carboxyl functional groups to permit stable bioconjugation to the amine groups of most biological targets. The primary antibodies were then covalently stained on the surface of the functional magnetic nanoparticles, followed by the analyte and secondary antibodies, resulting in a sandwich-type (antibody-antigen-antibody/enzyme) immune complex. The secondary antibodies were labeled with horseradish peroxidase for the catalytic oxidation of 2-aminophenol to yield electrochemically reducible molecules. The separation using an external magnetic field guaranteed fast and reliable purification and enrichment of analytes. Quantitative analysis was performed upon representative clinical targets: Hepatitis B surface antigen and α-fetoprotein in human serum. The detection limits were 0.06 ng/mL for the former and 0.5 ng/mL for the latter, which were about 10 times lower than values obtained by conventional enzyme-linked immunosorbent assays. The reported method may be adopted as a general strategy for the sensitive and selective determination of additional proteins and biological molecules.