Construction of nanozyme based with mixed valence manganese oxide loaded on defective metal-organic frameworks for sensitive detection of biomarker procalcitonin.

Nanozymes possess the advantages of high stability, adjustable catalytic activity and simple preparation processes, which position them as a promising alternative to natural enzymes. In this work, an oxidase-like nanozyme has been prepared by loading mixed valence manganese oxides (MnO) on defective PCN-224 MOFs (dPCN). Dodecanoic acid was utilized to introduce abundant mesoporous defects into the dPCN, allowing manganese oxide to grow in situ on the surface and within the pores. The mixed valence state of manganese oxides endowed the MnO@dPCN nanozyme (MdP) with redox and catalytic properties, and the high oxidase-like catalytic performance of MdP for TMB substrate also originated from its favorable electrical conductivity and affinity to the substrate. The reactive oxygen species of the catalytic reaction were mainly singlet oxygen (O) and peroxyl radicals (·O). Without the existence of hydrogen peroxide (HO), the nanozyme can rapidly and efficiently oxidize TMB substrate into blue oxidation state, which has strong absorbance at 650 nm. An immunosensor for detecting biomarker procalcitonin (PCT) in human serum samples has been established based on the high catalytic property of MdP nanozyme. The immunoassay for PCT has satisfactory accuracy and repeatability, and its linear detection range can reach to be 0.05-100 ng mL with a limit of detection (LOD) of 0.011 ng mL. The result affords a promising idea to construct oxidase-like nanozyme, and provides a method for sensitive determination of PCT in complex matrices.