Electrochemical immunoassay of hepatitis B surface antigen by the amplification of gold nanoparticles based on the nanoporous gold electrode

We describe herein the combination of electrochemical immunoassay using nanoporous gold (NPG) electrode with horseradish peroxidase (HRP) labeled secondary antibody-gold nanoparticles (AuNPs) bioconjugates for highly sensitive detection of protein in serum. The electroactive product of o-phenylenediamine (OPD) oxidized with H₂O₂ catalyzed by HRP was reduced in the Britton-Robinson (BR) buffer and the peak current of which was used to determine the concentration of antigen (Ag) in the analyte. The active surface area of NPG electrode was larger than that of a bare flat one. The presence of AuNPs enhanced the immobilized amount of HRP labeled antibody (Ab), which improved the sensitivity of the immunoassay when used as the secondary antibodies. As a result of these two combined effects, the sensitivity of the immunoassay for the determination of target protein was increased significantly. Using hepatitis B surface antigen (HBsAg) as a model, we demonstrate a dose response in the range of 0.01-1.0 ng/mL with a detection limit of 2.3 pg/mL. Analytical results of several human serum samples obtained using the developing technique are in satisfactory agreement with those given by enzyme-linked immune-absorbent assays (ELISA). In addition, the technique was about 100 times more sensitive in the detection of HBsAg than ELISA. All these demonstrated the feasibility of the present immunoassay method for clinical diagnosis.