A label-free electrochemical immunosensor for sensitive detection of indole-3-acetic acid (IAA) was developed using gold nanoparticles (AuNPs) functionalized with horseradish peroxidase labeled immunoglobulins G (AuNPs-HRP-IgG) as signal amplification probe and rat monoclonal antibody against IAA as capture probe. AuNPs-HRP-IgG could be immobilized and through the interaction between 4-aminophenylboronic acid and a single N-glycosylation site, which exist in the CH2 domain of IgG. The electrochemical immunosensor was characterized by differential pulse voltammetry (DPV) in 0.1 M PBS (pH 7.4) containing Fe(CN)(6)(3-/4-) as redox probe. The decreased oxidation peak current of Fe(CN)(6)(3-/4-) was used to monitor the antibody-antigen interaction. The electrochemical immunosensor exhibited a linear range from 1 x 10(-9) to 5 x 10(-6) M with a limit of detection of 5.5 x 10(-10) M (S/N = 3). The proposed electrochemical immunosensor could well discriminate IAA from other phytohormones, such as gibberellin, abscisic acid and salicylic acid. In addition, IAA extracted from leaf of mung bean sprouts was detected using the developed immunosensor for evaluating its applicability, and the recovery was from 93.5% to 106.75%. (C) 2013 Elsevier Ltd. All rights reserved.