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 MnO2 nanosheets on the surface of terbium metal–organic frameworks (Tb–MOFs), MOF@MnO2 nanocomposites are prepared and the fluorescence of Tb–MOFs is quenched significantly by MnO2. Additionally, the hybrid nanoflowers are self-assembled by cholesterol oxidase (ChOx) and copper phosphate (Cu3(PO4)2·3H2O). Then a new strategy for cholesterol determination is developed based on MOF@MnO2 nanocomposites and hybrid nanoflowers. Cholesterol is oxidized under the catalysis of hybrid nanoflowers to yield H2O2, which further reduces MnO2 nanosheets into Mn2+. Hence, the fluorescence recovery of Tb–MOFs is positively correlated to the concentration of cholesterol in the range of 10 to 360 μM. The limit of detection (LOD) of cholesterol is 1.57 μM. 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.

Sustainable One-Pot Immobilization of Enzymes in/on Metal-Organic Framework Materials

“…Therefore, some authors have proposed covalent linking, via crosslinking with glutaraldehyde [24][25][26] or EDC/NHS [27,28]. Also, the inclusion of new components into the composites has been often proposed, either to impart magnetic properties allowing their facile separation from reaction media [27,29], or to protect the enzyme by incorporating macromolecules like polyvinyl alcohol hydrogels [30] or by in situ formed self-assembled hybrid nanoflowers [31].…”

Green nanobiocatalysts: enhancing enzyme immobilization for industrial and biomedical applications

“…Human immunodeficiency virus (HIV) DNA biomarkers can be detected using glucose oxidase ( Long et al, 2016 ). Notably, there is a glucose sensor that uses biofuel made from a mixture of HRP and GOx as catalytic energy ( Chansaenpak et al, 2021 ), although its application is determined by enzymatic activity and the stability of polystyrene nanostructures ( Long et al, 2016 ), gold ( Phiri, Mulder & Vorster, 2019 ; Xianyu et al, 2021 ), and manganese oxide ( Xu et al, 2021 ), which reduce sample manipulation, increase reaction velocity, and boost repeatability and reusability ( Ripoll et al, 2020 ). Hu et al (2019) developed a collaborative system consisting of liquid metal nanoparticles and glucose oxidase, referred to as “LM@GOX”.…”

Expanding the Scope of Nanobiocatalysis and Nanosensing: Applications of Nanomaterial Constructs

“… 98 Notably, there is a sensor for glucose that utilizes the catalytic energy derived from a combination of HRP and GOx as biofuel. 99 Although the enzymatic activity determines its implementation, the stability of nanostructures of polystyrene, 95 gold, 94 , 96 graphene, 99 or manganese oxide 97 allows a reduction in sample manipulation, improves the reaction velocity, and promotes repeatability and reusability. Intrinsic properties of nanostructures have also been used for detection.…”

“…The glutathione, an antioxidant molecule strongly related to several types of cancer, competes with the BSA which leads to the photobleaching of the nanostructure. 93 Similarly, functionalized nanostructures have been coupled with enzymes like horseradish peroxidase (HRP) to sense iodide levels in biological fluids; 94 with glucose oxidase (GOx) to detect HIV DNA biomarkers 95 and colorimetric determination of glucose levels; 96 with cholesterol oxidase (ChOx) for cholesterol concentration analysis; 97 or with alkaline phosphatase (ALP) for ATP determination. 98 Notably, there is a sensor for glucose that utilizes the catalytic energy derived from a combination of HRP and GOx as biofuel.…”