Copper(II)-coated Fe₃O₄ nanoparticles as an efficient enzyme mimic for colorimetric detection of hydrogen peroxide

The authors describe the preparation of Cu(II)-coated Fe₃O₄) nanoparticles (NPs) that possess excellent peroxidase-like activity. The NPs were formed by chelation between Cu(II) ions and the oxygen functional groups of sodium ligninsulfonate. The morphology and structure of the NPs were characterized by scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. The NPs have an average diameter of 220 nm. They are shown to be viable peroxidase mimics that can catalyze the oxidation of 3,3',5,5'-tetramethylbenzidine by hydrogen peroxide to produce a blue coloration. The findings were used to design a colorimetric assay that has a linear response in the 2.5 to 100 μM H₂O₂ concentration range and a 0.2 μM detection limit. The assay excels by its selectivity, high sensitivity, good selectivity, portability and cost efficiency. Graphical abstract Fe₃O₄-Cu²⁺ nanoparticles with excellent peroxidase-like activity were successfully prepared via a facile strategy, and then used to design a facile as well as sensitive colorimetric H₂O₂ sensor. The linear range and the detection limit were 2.5~100 μM and 0.212 μM.