Design of a hollow GOx@Cu2+–PA integrated nanozyme for self-cascading colorimetric sensing of glucose

Abstract

Immobilizing natural enzymes in the micropores of metal–organic frameworks (MOFs) can usually enhance their stability, but the micropore space easily restricts the full extension of the enzymes’ molecular conformation, thereby affecting their catalytic activity. To provide a solution, herein, a MOF material with hollow structures was constructed as a carrier for enzyme immobilization. Glucose oxidase (GOx) was firstly loaded into zeolite imidazolium ester skeleton-8 (ZIF-8) by coprecipitation (denoted as GOx@ZIF-8); then, the hollow GOx@Zn²⁺–PA composite was prepared through top-down etching with phytic acid (PA). Finally, Cu²⁺ was further introduced using a cation exchange strategy to synthesize the GOx@Cu²⁺–PA integrated nanozyme with dual catalytic activities of peroxidase-mimicking and GOx. A series of characterizations confirmed the formation of the hollow structure of GOx@Cu²⁺–PA and the effective encapsulation of GOx. More significantly, under the protection of the hollow Cu²⁺–PA multifunctional nanozyme, the immobilized GOx exhibited excellent stability and catalytic activity, and Cu²⁺–PA could work in synergy with the immobilized GOx to achieve a highly efficient cascade catalytic reaction. On this basis, a simple and efficient integrated enzyme sensing system was developed for the rapid detection of the glucose content in human serum samples. This study provides a new insight into the rational design and synthesis of integrated nanozymes.