Development of phosphonate modified Fe(1−x)MnxFe2O4 mixed ferrite nanoparticles: Novel peroxidase mimetics in enzyme linked immunosorbent assay

► A series of intrinsic peroxidase mimetics using MnIIxFeII1−xFeIII2O4 nanoparticles were fabricated by a simple and cheap method using Mn2+:Fe2+ variation. ► The enhanced peroxidase activity showed typical Michaelis-Menten kinetics. ► A modified immunoassay was employed for the detection of IgGs using PMIDA-MnII0.5FeII0.5FeIII2O4 nanoparticles. ► The detection level of mouse IgG was ten times lower than previous reports of magnetite-linked ELISA.