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

Abstract A highly facile and feasible strategy on the fabrication of advanced intrinsic peroxidase mimetics based on Mn 2+ doped mixed ferrite (Mn II x Fe II 1− x Fe III 2 O 4 ) nanoparticles was demonstrated for the quantitative and sensitive detection of mouse IgG (as a model analyte). Mn 2+ doped Fe 1− x Mn x Fe 2 O 4 nanoparticles were synthesized using varying ratios of Mn 2+ :Fe 2+ ions and characterized by the well known complementary techniques. The increase of Mn 2+ 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 Fe 3 O 4 . The calculated K m and K cat 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 Fe 1− x Mn x Fe 2 O 4 nanoparticles using phosphonomethyl immunodiacetic acid (PMIDA) to engineer PMIDA–Fe 1− x Mn x Fe 2 O 4 fabricated enzyme linked immunosorbent assay (ELISA). Results of both PMIDA–Fe 1− x Mn x Fe 2 O 4 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.