Magnetic Amine-Functionalized\nZIF‑8 with Hierarchical\nPores for Efficient Covalent Immobilization of α‑Amylase

The immobilization strategy between ZIF-8 and different\nenzymes\nhas focused on in situ encapsulation and pore infiltration, while\nthe surface attachment has been seldom reported because of less functional\ngroups on the ZIF-8 surface. Here, a magnetic amine-functionalized\nZIF-8 with hierarchical pores was designed for efficient covalent\nimmobilization of α-amylase (α-Amy). By using Fe3O4 nanoparticles as the core and ZIF-8 as the shell, followed\nby Au3+–Zn2+ exchange reaction and β-mercaptoethylamine\nmodification, the magnetic hollow ZIF-8 nanoparticle with amine groups\non the surface was synthesized. With the assistance of glutaraldehyde,\nan α-Amy-magnetic hollow ZIF-8 composite was prepared and fully\ncharacterized by scanning electron microscopy, transmission electron\nmicroscopy, Fourier transform infrared spectrometry, X-ray photoelectron\nspectroscopy, energy-dispersive X-ray spectroscopy element mapping\nanalysis, and vibration sample magnetometry. Then, the catalytic activity\nof immobilized α-Amy was explored with a Km of 2.307 mg/mL and Vmax of 0.506\nmg/mL·min, indicating excellent catalytic activity. The study\nabout stability and reusability demonstrated that the catalytic activity\nof immobilized α-Amy remained above 50% after 10 times of reuse.\nThus, the designed magnetic amine-functionalized ZIF-8 was verified\nto be a nice carrier for covalent enzyme immobilization.