An ultrasensitive electrochemical immunosensor platform with double signal amplification for indole-3-acetic acid determinations in plant seeds

A label-free electrochemical immunosensor for ultra-sensitive detection of indole-3-acetic acid (IAA), a very important phytohormone, has been developed in this work. The detection strategy was mainly based on 4-aminophenylboronic acid, magnetic nanoparticles functionalized with horseradish peroxidase-conjugated goat anti-rat immunoglobulin G (HRP-IgG-Fe3O4) and rat monoclonal antibody against IAA-modified gold nanoparticles (anti-IAA-AuNPs). HRP-IgG-AuNPs was covalently assembled on the electrode surface through the specific chemical reaction between boronic acid and the vicinal diol in HRP-IgG. Then, anti-IAA-AuNPs was further assembled on the electrode via the interaction between IgG and antibody. Through the dual amplification of HRP-IgG-Fe3O4 and anti-IAA-AuNPs, the trapping capacity of the immunosensor for IAA was significantly enhanced based on the promotion of the immunoreaction between antibody and antigen, which resulted in a large decrease of the electrochemical response of the redox probe, Fe(CN)(6)(3-), and an increase in sensitivity. The developed electrochemical immunosensor exhibited a wide linear range from 0.02 to 500 ng mL(-1) with a low detection limit of 0.018 ng mL(-1) (S/N = 3). Moreover, the proposed immunosensor showed acceptable selectivity, reproducibility, accuracy and stability. The IAA extracted from various seeds was successfully detected using the developed immunosensor. This assay method might provide an alternative strategy for the detection of various phytohormones.