Enzyme Immobilization Using Two Processing Methods Onto Silica Core-Shell Particles

Two methods of enzyme immobilization onto silica core-shell particles were developed. The first method involved the immobilization of Candida rugosa lipase inside a previously synthe-sized mesoporous silica layer (deposited at 80 degrees C) surrounding a dense silica core. To prevent lipase leakage from the support, an outer mesoporous silica layer was deposited at 40 degrees C around the first silica layer containing the immobilized lipase. The deposition of the sec-ond layer was performed at a relatively lower temperature, to prevent thermal inactivation of the immobilized enzyme. The internal silica layer was obtained by assembling primary silica nanoparticles generated from highly basic sodium silicate solution at 80 degrees C on the surface of poly (diallyldimethylammonium chloride) (PDDA) functionalized silica core par-ticles. The average shell thickness and pore size of the internal silica layer was similar to 60 nm and 24 nm, respectively. The effect of process parameters on generation and aggregation of sil-ica nanoparticles prepared from highly basic sodium silicate solution was also investigated. The aggregation of silica particles generated at 40 degrees C and 80 degrees C took place after 840 s and 570 of reactions, respectively. The immobilization efficiency of lipase on the mesoporous silica monolayer was 80%. A decline of immobilized lipase activity was approximately 6 times after 10 reaction cycles due to lipase leakage from the monolayered shell. An outer mesoporous silica layer was deposited at 40 degrees C onto the surface of previously PDDA-functionalized mono-layered silica core-shell particles containing the immobilized lipase. The average thickness and pore size of outer mesoporous silica layer was similar to 60 nm and 17 nm, respectively. The activity of lipase immobilized inside the bilayered shell was further reduced due to diffu-sion resistance within the outer silica layer and PDDA layer however, it was retained for the next reaction cycles. The pore size of mesoporous silica layer obtained at 80 degrees C was insufficient to allow inver-tase immobilization. Thus, the second method for the immobilization of invertase was developed. It involved the preparation of the mesoporous silica layer simultaneously with invertase immobilization at 40 degrees C. The immobilized invertase showed decreased activity, but it was not hampered by substrate inhibition, as in the case of the free enzyme, due to the location of the enzyme inside the mesoporous silica layer, where the mass transfer resistance for the substrate to the enzyme active site was present. (C) 2020 SECV. Published by Elsevier Espana, S.L.U.