Apoferritin nanoparticle: a novel and biocompatible carrier for enzyme immobilization with enhanced activity and stability

Apoferritin is a uniform spherical nano-size biomaterial with excellent bio-compatibility. In this work, we report the use of apoferritin as a novel biocompatible carrier for stabilizing enzymes and enhancing their activities. We used glucose oxidase (GOx) as a model enzyme in this study. GOx was immobilized on the surface of the apoferritin through a green synthetic approach, taking advantage of bioaffinity binding between streptavidin and biotin. As a result, a glucose oxidase-biotin/streptavidin/biotin-apoferritin conjugate (Apo-GOx) was prepared using streptavidin as the bridge. The synthesized Apo-GOx was characterized by transmission electron microscopy, ultraviolet and fluorescence spectroscopy. The activity and stability of GOx on the surface of the apoferritin were investigated and challenged by different environmental factors, such as the temperature, chemicals and pH, in comparison with the biotinylated GOx (B-GOx). The results demonstrate that the activity of Apo-GOx is significantly enhanced while the thermal and chemical stabilities of Apo-GOx are also greatly improved compared to free B-GOx. For instance, the activity of the Apo-GOx only lost 30% after 2 h incubation at 50 oC in comparison to a 70% loss of free B-GOx. The activity of Apo-GOx remains intact after 30 min incubation in 5 M urea solution while B-GOx lost 80% activity after the same treatment. Furthermore, glucose detection was used as a model application for the enzyme immobilization method developed in this work. The GOx immobilized apoferritin nanoparticles exhibited high sensitivity for glucose detection with a detection limit of 3 nM glucose. This work offers a novel approach for immobilizing enzymes with enhanced stability and activity, thus holds the promising advantage for a number of applications, such as in enzyme catalysis, DNA assays and immunoassays.