Sensitive amperometric immunosensor for α-fetoprotein detection based on multifunctional dumbbell-like Au-Fe3O4 heterostructures

An ultrasensitive sandwich-type amperometric immunosensor for the detection of cancer biomarker, α-fetoprotein (AFP), was fabricated using Au/chitosan modified glassy carbon electrode (GCE) and antibody-functionalized dumbbell-like Au-Fe3O4 heterostructures as sensing platform and immuno-labels, respectively. The sensing platform was constructed by modifying GCE surface with chitosan and Au nanoparticles (NPs) for effective immobilization of primary antibody (Ab1). To fabricate the labels, nano-Au NPs were first epitaxially growth onto Fe3O4 surface to form the dumbbell-like Au-Fe3O4 followed by conjugation of secondary antibody (Ab2) onto Au surface (Au-Fe3O4-Ab2). Results showed that the GCE modified with chitosan produced high electrochemical response by conjugation of more Au-Ab1 and the dumbbell-like Au-Fe3O4 served as a dual-probe to immobilize Ab2 onto Au as well as to reduce H2O2 by Fe3O4, resulting in enhancement of signal amplification. Under the optimal condition at pH 6.5 and 30 °C, the prepared Au-Fe3O4/Ab2/AFP/Ab1/Au/chitosan/GCE immunosensors exhibited a good analytical performance in the presence of 10 mM H2O2 with wide dynamic range of 4 orders of magnitude (0.01–40 ng mL−1) and low detection limit of 2.3 pg mL−1. In addition, the proposed immunoassay also displayed good reproducibility and storage stability. Results obtained in this study clearly demonstrate that the Au-Fe3O4/Ab2/AFP/Ab1/Au/chitosan/GCE immunosensor is a promising biosensing platform for highly sensitive detection of AFP and various tumor makers.