Ultrasensitive electrochemical immunosensors for clinical immunoassay using gold nanoparticle coated multi-walled carbon nanotubes as labels and horseradish peroxidase as an enhancer

Abstract

A novel electrochemical immunosensor for the ultrasensitive detection of α-fetoprotein (AFP) is described with the use of a gold nanoparticle/(3-mercaptopropyl) trimethoxysilane modified electrode as a desirable platform and gold nanoparticle functionalized multi-walled carbon nanotube (MWCNT) nanocomposite labeled secondary antibodies (Ab₂) as a signal tag. At first, gold nanoparticles (AuNPs) were attached on the MWCNTs surface using poly(diallyldimethylammoniumchloride) (PDDA) as a linkage reagent to obtain AuNP–MWCNT nanocomposites. Subsequently, horseradish peroxidase (HRP) and thionine (Thi) labeled secondary antibodies (Thi-Ab₂) were used to bind AuNP–MWCNT nanocomposites with a high load amount and good biological activity. Moreover, the immunosensor can provide amplified signals because of the increased surface area and biocompatibility of AuNP–MWCNT nanocomposites. On the other hand, the AuNP functionalized (3-mercaptopropyl) trimethoxysilanes (MPTS) were used for the biosensor platform to increase the surface area as well as improving the electronic transmission rate to capture a large amount of primary antibodies (Ab₁). Thus, amplified signals can be obtained by an electrochemical sandwich immunoassay protocol in the presence of H₂O₂. The proposed sensing strategy provides a wide linear dynamic range from 0.01 to 50 ng mL⁻¹ with a low detection limit of 3 pg mL⁻¹ (S/N = 3). Significantly, the developed immunoassay method showed a good stability, selectivity and reproducibility.