Preparation and characterization of amino and carboxyl functionalized core-shell Fe3O4/SiO2 for L-asparaginase immobilization: A comparison study

Magnetic nanoparticles are well known as facile and effective support for enzyme immobilization since they have a high surface area, large surface-to-volume ratio, easy separation, a fast and high enzyme loading. This study aims to provide insights on whether acidic or basic modified particles are more effective for L-asparaginase (ASNase) immobilization. Therefore, amino (Fe3O4/SiO2/NH2) and carboxyl-functionalized (Fe3O4/SiO2/COOH) particles were prepared. The functional groups, crystalline structure, magnetic properties, morphology, chemical composition and thermal behaviour of the prepared modified nanoparticles were examined via Fourier-transform infra-red spectroscopy (FTIR), X-ray diffraction (XRD), vibrating-sample magnetometer (VSM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX). Under the optimum conditions, the immobilized enzymes were more stable within a certain range of temperatures and pH values in comparison to free enzyme. On the other hand, the immobilized enzymes showed greater stability after incubation for 3 h at 50 °C. The free enzyme maintained only 30% of its initial activity for 4 weeks at 4 °C, while Fe3O4/SiO2/NH2/ASNase and Fe3O4/SiO2/COOH/ASNase retained more than 78.9% and 56.5% of initial activities under the same conditions, respectively. Moreover, Fe3O4/SiO2/NH2/ASNase (77.2%) and Fe3O4/SiO2/COOH/ASNase (57.4%) displayed excellent operational stability after 17 repeated cycles. These findings suggested that the Fe3O4/SiO2/NH2 and Fe3O4/SiO2/COOH may be utilized as efficient and sustainable supports to developed immobilized ASNase in several biotechnological applications.