Label-free amperometric immunosensor based on antibody immobilized on a positively charged gold nanoparticle/l-cysteine-modified gold electrode

Positively charged gold nanoparticles prepared in organic solvents were used for the first time to fabricate a label-free amperometric immunosensor for rapid immunoanalysis. To construct the sensor, positively charged gold nanoparticles are adsorbed on the surface of a l-cysteine modified electrode by electrostatic interaction. Then, the positively charged gold nanoparticle film formed is utilized as a template to immobilize anti-h-IgG for subsequent immunoreaction. Excellent electrocatalytic oxidation of ascorbic acid at the immunosensor is observed, which is utilized for signal amplification. Thus, the amperometric immunosensor can be used for the determination of h-IgG in the absence of label. After immunoreaction, the immobilization of bulk immunocomplex over the surface of the electrode is expected to retard the flux of ascorbic acid to the surface of the electrode, which leads to a linear decrease in amperometric response over the range of 0.5-25 ng mL(-1). Moreover, the mechanism for the electrocatalytical response of the immunosensor, the characteristics, and the optimal conditions for amperometric immunoanalysis of h-IgG are studied.