Robust enzyme-iron oxide nanoparticle composites entrapped in mesoporous silica nanospheres and their properties

Effective preservation of enzyme activity is required for using immobilized enzymes to catalyze reactions. To this end, the co-immobilization of an enzyme and nanoparticles in a nanosphere system using a reverse microemulsion is proposed. Iron oxide nanoparticles (MNPs) and carboxyl esterase (CE) were encapsulated in spherical mesoporous silica nanospheres. After immobilization, the encapsulated CE retained approximately 10.9% of the specific activity of free CE for the hydrolysis reaction. Regarding its stability during storage, the immobilized CE retained 52% and 30% of its initial activity after 30 days at 25 °C and under rigorous incubation conditions, respectively. Utilizing this magnetically separable property enabled the immobilized CE to be recycled 13 times through easy magnetic separation. The encapsulation of CE in silica nanospheres improved the efficiency of the enzymatic reactions by reducing the mass transfer limitation without any structural changes upon immobilization. This is the first demonstration of the co-encapsulation of MNPs and enzymes in mesoporous silica nanospheres to form stabilized and immobilized enzyme systems for biocatalytic applications.