Amperometric immunoassay for the detection of Salmonella pullorum using a screen - printed carbon electrode modified with gold nanoparticle-coated reduced graphene oxide and immunomagnetic beads

The article describes a sandwich electrochemical immunoassay for detecting the food pathogen Salmonella pullorum (S. pullorum). The assay is based on the use of immunomagnetic beads (IMB) and reduced graphene oxide coated with gold nanoparticles (rGO/AuNPs) acting as an electrochemical label. The IMB were prepared via conjugation of antibody against S. pullorum (Ab1) to silica coated magnetic beads (SiO2/Fe3O4) and were used to capture S. pullorum from the sample. The rGO/AuNP were prepared by co-reduction of chloroauric acid and graphene oxide and then linked to secondary antibody (Ab2). This conjugate served as a label in a sandwich immunoassay to produce signals. The electrochemical immunoassay was carried out by immobilizing the rGO/AuNP/Ab2/S/IMB complex on a four channel screen-printed carbon electrode (4-SPCE). The assay involves the following steps: (a) Exposure of the modified 4-SPCE to the sample; (b) Electro-oxidation of the modified 4-SPCE in 0.2 M HCl; and (c) Differential pulse voltammetry (DPV). It is found that the use of the rGO/AuNP leads to strong signal amplification. The DPV signal (at an optimal working potential of +1.25 V vs. Ag/AgCl for 120 s) is linearly related to the logarithm of the concentration of S. pullorum in the range from 102 to 106 CFU⋅mL‾1. The detection limit is as low as 89 CFU⋅mL‾1. This nanoparticle-based immunoassay excels by its low cost and ease of operation, thereby providing a promising tool in clinical analysis.