MOF@MnO2 nanocomposites prepared using in situ method and recyclable cholesterol oxidase–inorganic hybrid nanoflowers for cholesterol determination

Abstract In this work, through the in situ growth of MnO 2 nanosheets on the surface of terbium metal–organic frameworks (Tb–MOFs), MOF@MnO 2 nanocomposites are prepared and the fluorescence of Tb–MOFs is quenched significantly by MnO 2 . Additionally, the hybrid nanoflowers are self-assembled by cholesterol oxidase (ChOx) and copper phosphate (Cu 3 (PO 4 ) 2 ·3H 2 O). Then a new strategy for cholesterol determination is developed based on MOF@MnO 2 nanocomposites and hybrid nanoflowers. Cholesterol is oxidized under the catalysis of hybrid nanoflowers to yield H 2 O 2 , which further reduces MnO 2 nanosheets into Mn 2+ . Hence, the fluorescence recovery of Tb–MOFs is positively correlated to the concentration of cholesterol in the range of 10 to 360 μ M. The limit of detection (LOD) of cholesterol is 1.57 μ M. On the other hand, the hierarchical and confined structure of ChOx–inorganic hybrid nanoflowers greatly improve the stability of the enzyme. The activity of hybrid nanoflowers remains at a high level for one week when stored at room temperature. Moreover, the hybrid nanoflowers can be collected by centrifugation and reused. The activity of hybrid nanoflowers can continue at a high level for five cycles of determination. Therefore, it can be concluded that the hybrid nanoflowers are more stable and more economic than free enzymes, and they show a similar sensitivity and specificity to cholesterol compared with free ChOx. Finally, this strategy has been further validated for the determination of cholesterol in serum samples with satisfactory recoveries.