SUMMARY: Nanotechnology is important for medical diagnosis. Various nanoparticles have presented tremendous potential for diagnosing disease markers, pre-cancerous cells, fragment of viruses, specific proteins, antibodies, and other disease indicators. In general, nanoparticles are smaller than 1,000 nm and produced from different materials in different shapes such as spheres, rods, wires, and tubes. Our study aimed to develop a novel antigen-capture immunoassay based on IgG polyclonal antibody-coated magnetic microbead nanoparticles for the rapid detection of circulating surface antigen 1 of Toxoplasma gondii in human serum samples. Sandwich ELISA elicited a sensitivity of 92z, a specificity of 92.7z, a positive predictive value (PPV) of 92z, and a negative predictive value (NPV) of 92.7z. Immunomagnetic bead-ELISA showed sensitivity (98z), specificity (96.4z), PPV (96z), and NPV (98.1z) higher than that of sandwich ELISA. It is obvious that the use of magnetic microbead nanoparticles offers the potential advantage of improving the diagnostic testing of toxoplasmosis.