Peroxidase Labeled Antibody Conjugated Gold Nanoparticles for Ultrasensitive Voltammetric Immunosensing

An electrochemical immunosensing platform capable of detecting Immunoglobulin G (IgG) concentration as low as femtograms was developed based on signal amplification strategy. The immunosensing platform was fabricated using self-assembled monolayers (SAM) of 11mercaptoundecanoic acid (MUDA) on a gold disc electrode. The covalent immobilization of antibody was achieved through the bonding of a carboxyl group of MUDA and amino group of antibody using [1-ethyl-3-(3-dimethylaminopropyl) carbodiimide] (EDC) and N-hydroxysuccinimide (NHS) chemistry. The formation of SAM and antibody immobilization was analyzed using cyclic voltammetry and electrochemical impedance spectroscopy. The gold nanoparticles conjugated with horseradish peroxidase-labeled secondary antibodies were used as nanolabels, to increase the sensitivity and catalytic efficiency of the immunosensor. The sandwich immunocomplex formed on the electrode surface produced an electrocatalytic response through the reduction of hydrogenperoxide in the presence of thionin. The fabricated immunosensor exhibited two linear ranges that included IgG concentrationsof 10 fg mL
^-1
to 0.1 ng mL
^-1
and 0.1 to 100 ng mL
^-1
respectively.