An amperometric immunosensor based on new thiolated bionanocomposite with a high dispersion of gold nanoparticles (AuNPs) for the sensitive detection of indole-3-acetic acid (IAA) is being reported herein. Briefly, a thiolated nanocomposite was prepared via the microwave-assisted thiol-ene reaction of 2,5-dimercapto-1,3,4-thiadiazole (DMcT) with oxidized polyaniline (PANI), which was synthesized in the presence of multiwalled carbon nanotubes (MWCNTs), yielding thiolated polyaniline (TPANI)-MWCNTs. Further, AuNPs were deposited on the TPANI-MWCNTs by microwave-assisted method to obtain a AuNPs/TPANI-MWCNTs nanocomposite. Finally, the thiolated bionanocomposite film was constructed via the specific chemical reaction between boronic acid functionalized AuNPs and the vicinal diol functionalized AuNP labeled immunoglobulin G (IgG-AuNPs). The change in the reduction peak current of Fe(CN)₆ ^3- was used to monitor the immunoreaction between IAA and antibody. The TPANI-MWCNT nanocomposites uniformly disperse AuNPs, IgG-AuNPs and anti-IAA-AuNPs, leading to the amplification of the signal of the immunosensor. Fourier transform infrared spectra (FTIR), cyclic voltammetry (CV), transmission electron microscopy (TEM), ultraviolet visible spectroscopy (UV-vis) and differential pulse voltammetry (DPV) were used to characterize the nanocomposite film and the stepwise modification of the immunosensor. The prepared thiolated bionanocomposite material has good biocompatibility, a highly uniform dispersion of the AuNPs with a narrow size distribution as verified by TEM, and high load/activity of the immobilized antibody proved via DPV. The fabricated IAA amperometric immunosensor not only exhibits a good linear arrange from 1.0 pg mL^-1 to 10 ng mL^-1 with the limit of detection of 0.97 pg mL^-1 (S/N = 3), but also possesses good selectivity, reproducibility and stability for the detection of IAA.

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