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

A highly facile and feasible strategy on the fabrication of advanced intrinsic peroxidase mimetics based on Mn2+ doped mixed ferrite (MnIIxFeII1−xFeIII2O4) nanoparticles was demonstrated for the quantitative and sensitive detection of mouse IgG (as a model analyte). Mn2+ doped Fe1−xMnxFe2O4 nanoparticles were synthesized using varying ratios of Mn2+:Fe2+ ions and characterized by the well known complementary techniques. The increase of Mn2+ proportion had remarkably enhanced the peroxidase activity and magnetism. The catalytic activity of mixed ferrites was found to follow Michaelis–Menten kinetics and was noticeably higher than native Fe3O4. The calculated Km and Kcat exhibited strong affinity with substrates which were remarkably higher than similar sized native magnetite nanoparticles and horseradish peroxidase (HRP). These findings stimulated us to develop carboxyl modified Fe1−xMnxFe2O4 nanoparticles using phosphonomethyl immunodiacetic acid (PMIDA) to engineer PMIDA–Fe1−xMnxFe2O4 fabricated enzyme linked immunosorbent assay (ELISA). Results of both PMIDA–Fe1−xMnxFe2O4 linked ELISA revealed that the enhancements in absorbance during the catalysis of enzyme substrate were linearly proportional to the concentration of mouse IgG within the range between 0.1 μg/ml and 2.5 μg/ml. Further, this detection was ten times lower than previous reports and the detection limit of mouse IgG was 0.1 μg/ml. The advantages of our fabricated artificial peroxidase mimetics are combined of low cost, easy to prepare, better stability and tunable catalytic activity. Moreover, this method provides a new horizon for the development of promising analytical tools in the application of biocatalysis, bioassays, and bioseparation.