Magnetic-core@dual-functional-shell nanocomposites with peroxidase mimicking properties for use in colorimetric and electrochemical sensing of hydrogen peroxide

A self-sacrificing catalytic method is described for the preparation of magnetic core/dual-functional-shell nanocomposites composed of magnetite, gold and Prussian Blue (type Fe3O4@Au-PB). Two reaction pathways are integrated. The first involves chemical dissolution of Fe3O4 (the self-sacrificing step) by acid to release ferrous ions which then reacts with hexacyanoferrate(IV) to generate PB in the proximity of the magntic nanoparticles (MNPs). The second involves the reduction of tetrachloroaurate by hydroxylamine to generate gold under the catalytic effect of the MNPs. At the end, the MNPs@Au-PB nanocomposite is formed. This method exploits both the chemical reactivity and catalytic effect of the MNPs in a single step. The multi-function material was applied (a) in an optical assay for H2O2; (b) in an amperometric assay for H2O2; (c) in an enzymatic choline assay using immobilized choline oxidase. The limit of electrochemical detection of H2O2 (at a potential as low as 50 mV) is 1.1 μM which is comparable or better than most analogous methods. The sensors display superior performance compared to the use of conventional core@single-shell (MNPs@PB) nanomaterials.