A Sandwich-type Amperometric Immunosensor Based on One-dimensional Assembly of Magnetic DNA Nanoprobes

A new type of one-dimensional magnetic nanoprobe was fabricated based on a DNA chain fixed with numerous Fe3O4 (core)/ZrO2 (shell) nanomagnetic beads (ZMPs) modified with horseradish peroxidase (HRP)-labeled anti-α-fetoprotein secondary antibody (AFPAb2). An electrochemical immunosensor for AFP was developed using the nanoprobe DNA/(ZMPs-HRP-AFPAb2)n and AFP-antibody (AFPAb1)-immobilized glassy carbon electrode (GCE) modified with nanogold. A sandwich-type immunocomplex could be formed between the immobilized AFPAb1 on the GCE, the AFP sample, and the probe DNA/(ZMPs-HRP-AFPAb2)n; moreover, the linked HRP on the probes could catalyze the electrochemical reaction of carbamide peroxide in the presence of hydroquinone. Under optimal conditions, the immunosensor response showed a linear relationship with the AFP concentration in the range 0.01–25 μg L−1, with a detection limit of 4 ng L−1. The immunosensor was used to determine the AFP level in serum samples, and the results were satisfactory. The proposed amperometric immunosensor was sensitive, provided a rapid detection, and was controllable by a magnetic field. This study provides a strategy for the one-dimensional assembly and development of highly sensitive immunosensors.