Magnetic Amine-Functionalized ZIF-8 with Hierarchical Pores for Efficient Covalent Immobilization of α-Amylase

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