Preparation of amine-functionalized mesoporous magnetic colloidal nanocrystal clusters for glucoamylase immobilization

• Mesoporous carboxyl-functionalized magnetic colloidal nanocrystal clusters (MCNCs) were synthesized.
• The mesoporous MCNCs showed large surface area and high magnetization.
• The sizes of the MCNCs could be easily tuned by varying the surfactant concentration.
• The amine-functionalized mesoporous MCNCs were utilized to immobilize enzyme.

A facile one-pot synthesis of size-tunable mesoporous carboxyl-functionalized magnetic colloidal nanocrystal clusters (MCNCs) with high magnetization (82.0 emu/g), large surface area (95 m2/g), and excellent colloidal stability has been developed. The mesostructured MCNCs were synthesized by a solvothermal approach with iron (III) chloride hexahydrate as a precursor, ethylene glycol as a reducing agent, ammonium acetate as a porogen, and ethylenediaminetetraacetic acid disodium salt (EDTA-2Na) as a surface-modification agent. Glucoamylase was immobilized onto the mesoporous MCNCs via the different routes. These immobilized glucoamylase exhibited excellent thermal stability and reusability in comparison with the free enzyme. The residual activity of immobilized enzyme remained above 65% after 6 h, while free glucoamylase was only left over 45% of the initial activity. And the residual activity of the immobilized enzyme was about 60% of the initial activity after the 10th reuse.