A novel immunosensor for detecting toxoplasma gondii-specific IgM based on goldmag nanoparticles and graphene sheets

A novel electrochemical immunosensor for detecting toxoplasma gondii-specific IgM (Tg-IgM) was constructed based on goldmag (Au–Fe3O4) nanoparticles and graphene sheets (GS). Thionine (Thi), as a mediator, was first electropolymerized on a nafion-GS (Nf-GS) modified electrode. Subsequently, gold nanoparticles (AuNPs) were attached onto the poly-thionine film through π-stacking interactions, and then were used to immobilize toxoplasma gondii antigen (Tg-Ag) for immunosensor fabrication. A sandwich-type immunoassay for Tg-IgM was performed using Au–Fe3O4 labeled anti-IgM-horseradish peroxidase (HRP) as trace label. Electrochemical detection was carried out in the presence of H2O2 as HRP substrate. Using Au–Fe3O4 provided a simple, non-chemical damaging method for regeneration, and enhanced the HRP reduction ability toward H2O2. The AuNPs/Thi/Nf-GS nanocomposite also had good conductivity and biocompatibility, which effectively improved the immunosensor sensitivity. Under optimal conditions, the immunosensor can detect Tg-IgM in two linear ranges from 0.0375 to 1.2 AU mL−1 and from 2.0 to 18 AU mL−1 with a detection limit of 0.016 AU mL−1 (S/N = 3). The immunosensor exhibited good reproducibility, stability, and selectivity as well.