Design And Synthesis Of Novel Magnetic Nanomaterials For Lipase Immobilization

Magnetic nanomaterials become a research hotspot in recent years and widely used in biosynthesis, organic catalysis, drug delivery, data storage and environmental improvement, due to their high specific surface area, special magnetic behavior, excellent chemical durability and biocompatibility. Design and synthesis of novel magnetic nanomaterials with unique properties for lipase immobilization, can improve the disadvantage of the free lipase such as difficulty of product recovery and impossibility of multiple reuse. The main research results of this dissertation are as follows:1. Solvothermal synthesis of monodisperse functionalized magnetic nanoparticles for lipase immobilizationA simple and highly efficient method was proposed for immobilization of porcine pancreas lipase on magnetic nanoparticles. Monodisperse Fe3O4magnetic nanoparticles were synthesized by solvothermal reduction and surface-modified by aminopropyltriethoxysilane. Lipase was covalently immobilized on the obtain particles using glutaraldehyde as a coupling agent. SEM, TEM, XRD, FT-IR, TGA and VSM were used to characterize the Fe3O4magnetic nanoparticles. Magnetic nanoparticles showed outstanding monodispersity and magnetic response. The performance of the immobilized enzymes was also studied, and the protein content and activity recovery of the immobilized enzymes were up to120mg/g and54.8%. The immobilized lipases exhibited excellent thermal stability, and could be reused10times with the activity remained above90%. This study provided a simple, efficient, green and economical method and expected to be widely applied in the immobilization of enzymes.2. One-pot synthesis of water-dispersible size-tunable magnetite nanocrystal clusters for lipase immobilizationThis work developed a one-pot synthesis of water-dispersible size-tunable Fe3O4magnetite nanocrystal clusters functionalized with amino or carboxyl groups by a solvothermal reduction reaction. Dopamine and3,4-dihydroxyhydroxycinnamic acid were used as both surfactant and interparticle linker for economical and environment-friendly purposes. Morphology, chemical composition and magnetic properties of the prepared particles were investigated by several methods including SEM, TEM, XRD, XPS, FT-IR, Raman, TGA, Zeta-potential and VSM. The sizes of particles could be easily tuned over a wide range of175-500nm by varying the surfactant concentration. Moreover, ethylene glycol/diethylene glycol mix solvents with different ratios were acted as reductants to obtain the particles with smaller sizes. The nanoparticles exhibited superior magnetic properties and high colloidal stability in water. To estimate the applicability of the obtained magnetite nanocrystal clusters in bio-related fields, Candida rugosa lipase was selected for the enzyme immobilization process. The immobilized lipase exhibited excellent thermal stability and reusability in comparison with free enzyme. This novel strategy would simplify the reaction protocol which offered new potential applications in biotechnology and organocatalysis.3. Polylol reduction synthesis of Fe3O4/Graphene hybrids for lipase immobilizationThis work reported a polylol reduction approach on the preparation of the Fe3O4/Graphene hybrids for immobilizing porcine pancreatic lipase. The Fe3O4/Graphene hybrids were characterized by several methods. By adjusting precursor composition and optimizing reaction conditions, we investigated the effect of properties of the Fe3O4/Ggraphene hybrids on the activity of immobilized lipase. The Fe3O4/Graphene hybrids exhibited excellent magnetic behavior, chemical durability and biocompatibility. Moreover, porcine pancreatic lipases immobilized on Fe3O4/Graphene hybrids become magnetically recyclable and have a remarkable catalytic activity and thermal stability. The effect of pH value, temperature and denaturant was also investigated. This synthesis method of Fe3O4/Graphene hybrids for enzyme immobilization opened a unique green and sustainable application approach.4. Synthesis of PAMAM-dendrimer modified magnetic nanoparticles for lipase immobilizationUniform-size monodisperse functionalized Fe3O4magnetic nanoparticles were synthesized by solvothermal method. The PAMAM-dendrimer was covalently grafted on the magnetic nanoparticles to prepare three generation PAMAM modified magnetic carriers. SEM, TEM, XRD, FT-IR, TGA and VSM were used to characterize the prepared materials. Candida rugosa lipases were covalently immobilized on the carriers using glutaraldehyde as a coupling agent. Various properties of the immobilized enzyme were studied such as pH, temperature and denaturant. The immobilized lipase exhibited excellent thermal stability and reusability in comparison with free enzyme. The hyperbranched strategy effectively improved the surface performance of magnetic nanoparticles and the functional efficiency of the carriers, which expected to be widely used in biomedical field.