An electrochemical impedance immunosensor with signal amplification based on Au-colloid labeled antibody complex

A highly sensitive electrochemical impedance immunosensor was developed by using a novel amplification procedure with the application of a Au-colloid labeled antibody as the primary amplifying probe and a multistep amplification by alternating treatment of the resulting assembly with a Au-colloid labeled secondary antibody and a Au-colloid labeled antibody. The rabbit anti-human IgG antibody was immobilized through a self-assembled colloidal Au layer on the gold electrode. The analyte, human IgG, was detected through the impedance measurements with the sensing interface modified by the rabbit anti-human IgG antibody. In the primary amplification, the Au-colloid labeled goat anti-human IgG antibody was used to amplify the electron-transfer resistance resulting from the binding of the antigen to the immunosensor surface. A further amplification was performed through sequential binding of the Au-colloid labeled rabbit anti-goat IgG antibody and the Au-colloid labeled goat anti-human IgG antibody. The impedance increments were observed to be linearly dependent upon the IgG concentration in the range of 15.3–328.3 ng L−1 with a detection limit of 4.1 ng L−1.