No abstract

The development of new methods for fabricating artificial multienzyme systems has attracted much interest because of the potential applications and the urgent need for multienzyme catalysts. Controlling the enzyme ratio is critical for improving the cooperative enzymatic activity in multienzyme systems. Herein, we introduce a versatile strategy for fabricating a multienzyme system by coimmobilizing horseradish peroxidase (HRP) and glucose oxidase (GOx) on magnetic nanoparticles multifunctionalized with dopamine derivatives through DNA-directed immobilization. This multienzyme system exhibited precise enzyme ratio control, high catalytic efficiency, magnetic retrievability, and enhanced stability. The enzyme ratio was conveniently adjusted, as required, by regulating the quantity of functional groups on the multifunctionalized nanoparticles. The optimal mole ratio of GOx/HRP was 2:1. The Michaelis constant K and specificity constant (k/K, where k is the catalytic rate constant) of the multienzyme system were 1.41 mM and 5.02 s mM, respectively, which were approximately twice the corresponding values of free GOx&HRP. The increased bioactivity of the multienzyme system was ascribed to the colocalization of the involved enzymes and the promotion of DNA-directed immobilization. Given the wide variety of possible enzyme associations and the high efficiency of this strategy, we believe that this work provides a new route for the fabrication of artificial multienzyme systems and can be extended for a wide range of applications in diagnosis, biomedical devices, and biotechnology.

Although capsule-like materials as host carriers for enzyme encapsulation have been a hot topic in recent years, creating an ideal microenvironment for enhanced enzymatic performance is still a formidable challenge. Herein, we created a template-free method to in situ encapsulate natural enzymes in hollow covalent organic framework (COF) capsules at room temperature. The COF crystallites migrated from the inner core and self-assembled at the outside walls during the inside-out Ostwald ripening process, retaining the enzymes in the cavity. The adjustable hollow structure of the enzyme@COF capsule allowed the basic vibration of the enzyme to maintain a certain degree of freedom, thus significantly enhancing the enzymatic bioactivity. The hollow enzyme@COF capsule has large mesoporous tunnels allowing the efficient transport. In addition, the enzyme encapsulated in the capsule showed superior activity and ultrahigh stability under various extreme conditions that may lead to enzyme inactivation, such as high temperature, organic solvents, chelates, and the denaturing agent. Finally, the prepared hollow GOx@COF capsule was used for electrochemical sensing of glucose in human serum, and the electrochemical sensor exhibited high selectivity and satisfactory test results. This research not only provides a new way for COFs to encapsulate enzymes but also has potential applications in biocatalysis and biosensing, making artificial organelles possible.

In recent years, metal–organic frameworks (MOFs) have been extensively studied as candidate enzyme immobilization platforms. However, conventional MOF–enzyme composites usually exhibit low controllability and reusability. In this study, a novel and stable strategy for enzyme immobilization was designed by use of ZIF-8 to encapsulate in situ DNA–enzyme composites on the surface of magnetic particles (MPs). The mechanism of in situ encapsulation was discussed in detail. It was found that immobilized enzymes were involved in the growth of ZIF-8, and the DNA cross-linking agents promoted the growth of ZIF-8 on the surface of MP. The thermal, chemical, and physical stabilities of horseradish peroxidase (HRP) were all significantly enhanced after in situ encapsulation. Most importantly, this strategy was proven to be a general platform that can be used to stabilize various proteins. The in situ encapsulation strategy was expanded to immobilize a cascade of enzymes, and ZIF-8@MPGOx–HRP possessed high selectivity and a wide linear range (25–500 μM) for glucose detection.

Nanozymes with various activities have attracted much attention owing to their great potential in the fields of biochemical analysis and environmental monitoring. Herein, for the first time, granular Co2V2O7 particles were synthesized using a simple hydrothermal method with pH regulation, and the triple-enzyme (oxidase-like, peroxidase-like, and catalase-like) activities and catalytic mechanisms of the prepared particles were systematically studied. On the basis of the excellent oxidase-like and peroxidase-like activities of Co2V2O7 particles, respectively, a colorimetric biosensor for detecting glutathione in health products (linear range: 2.5–20 μM) and a fluorescent platform for detecting glucose in human serum (linear range: 0.1–80 μM) were established, both of which had good selectivity and reliability. In particular, the fluorescence detection system exhibited ultrahigh sensitivity for H2O2, with a linear range of 0.008–3.2 μM, and a detection limit (0.002 μM) far superior to most reported in the literature to date. Furthermore, a one-step strategy for glucose detection was established to replace the traditional complicated two-step detection method, resulting in a more convenient detection process. These findings indicate the significant application prospects of Co2V2O7 particles in the field of biocatalysis and provide useful information for the future development of cobalt vanadate nanomaterials as enzyme mimics.