Fe₃O₄/Au magnetic nanoparticle amplification strategies for ultrasensitive electrochemical immunoassay of alfa-fetoprotein

Ning Gan^1*, Haijuan Jin^1*, Tianhua Li¹, Lei Zheng^2
1The State Key Laboratory Base of Novel Functional Materials and Preparation Science, Faculty of Material Science and Chemical Engineering, Ningbo University, Ningbo, ²Department of Laboratory Medicine, Nanfang Hospital, Southern Medical University, Guangzhou, People's Republic of China
^*Both authors contributed equally to this work

Background: The purpose of this study was to devise a novel electrochemical immunosensor for ultrasensitive detection of alfa-fetoprotein based on Fe₃O₄/Au nanoparticles as a carrier using a multienzyme amplification strategy.
Methods and results: Greatly enhanced sensitivity was achieved using bioconjugates containing horseradish peroxidase (HRP) and a secondary antibody (Ab₂) linked to Fe₃O₄/Au nanoparticles (Fe₃O₄/Au-HRP-Ab₂) at a high HRP/Ab₂ ratio. After a sandwich immunoreaction, the Fe₃O₄/Au-HRP-Ab₂ captured on the electrode surface produced an amplified electrocatalytic response by reduction of enzymatically oxidized hydroquinone in the presence of hydrogen peroxide. The high content of HRP in the Fe₃O₄/Au-HRP-Ab₂ could greatly amplify the electrochemical signal. Under optimal conditions, the reduction current increased with increasing alfa-fetoprotein concentration in the sample, and exhibited a dynamic range of 0.005–10 ng/mL with a detection limit of 3 pg/mL.
Conclusion: The amplified immunoassay developed in this work shows good precision, acceptable stability, and reproducibility, and can be used for detection of alfa-fetoprotein in real samples, so provides a potential alternative tool for detection of protein in the laboratory. Furthermore, this immunosensor could be regenerated by simply using an external magnetic field.

Keywords: Fe₃O₄/Au nanoparticles, alfa-fetoprotein, sandwich immunoassay, electrochemical immunosensor