Electrochemical sandwich immunoassay for Escherichia coli O157:H7 based on the use of magnetic nanoparticles and graphene functionalized with electrocatalytically active Au@Pt core/shell nanoparticles

A highly sensitive electrochemical sandwich immunoassay is described for determination of Escherichia coli O157:H7 (E. coli O157:H7). Silica coated magnetite nanoparticles (FeO) were modified with primary antibody to capture E. coli O157:H7. Gold-platinum core/shell nanoparticles (Au@Pt NPs) with different Pt shell thicknesses were prepared via changing the molar ratio of HPtCl to HAuCl in the precursor solution. The optimized Au@Pt NPs exhibit enhanced activity in the electrocatalytic reduction of hydrogen peroxide (HO). The Au@Pt NPs were modified with graphene that was functionalized with Neutral Red, and then used as an electrochemical label for secondary antibodies and horseradish peroxidase (HRP). The sandwich immunocomplexes were magnetically absorbed on a 4-channel screen printed carbon electrode. Due to the catalysis of the Au@Pt NPs and HRP, the signal is strongly amplified in the presence of HO when using thionine as the electron mediator. Under optimal conditions, the immunoassay has a linear response in the 4.0 × 10 to 4.0 × 10 CFU·mL concentration range, with a limit of detection of 91 CFU·mL (at an S/N ratio of 3). [Figure not available: see fulltext.].