Mesoporous silica spheres as supports for enzyme immobilization and encapsulation

We report the immobilization of various enzymes in mesoporous silica (MS) spheres followed by encapsulation via the layer-by-layer assembly of multilayered nanocomposite thin shells. A range of enzymes with different molecular sizes and isoelectric points (pI) (e.g., catalase, peroxidase, cytochrome C. and lysozyme) has been examined in MS particles with a series of pore sizes. MS spheres with a bimodal mesoporous structure (BMS, 2-3 nm and 10-40 nm) show faster immobilization rates and significantly improved enzyme immobilization capacity than similar particles with only the smaller mesopores. High enzyme loadings (20-40 wt %) and rapid uptake (several minutes) were observed in BMS spheres for enzymes with a molecular size less than or equal to 3 nm and pI greater than or equal to 10. Following immobilization of the enzyme catalase, multilayered polyelectrolyte (PE) [poly(diallyldimethylammonium chloride), PDDA/ poly(sodium 4-styrenesulfonate), PSS], or PE/nanoparticle [PDDA/silica nanoparticles, Si-NP] shells were deposited onto the enzyme-loaded spheres. The activity of the encapsulated catalase was retained, even after exposure to enzyme-degrading substances (e.g., proteases). Catalase also exhibits enhanced stability in reaction conditions over a wide pH range (pH 5-10) and retains an activity of 70% after 25 successive batch reactions, demonstrating the usefulness of the loaded particles in biocatalytic applications. The PDDA/PSS multilayer-encapsulated catalase in BMS spheres shows a lower activity than catalase encapsulated by PDDA/Si-NP multilayers. However, the enzyme possesses significantly enhanced reaction stability with increasing PDDA/PSS layer number, which might be caused by a reduced reaction rate. The approach presented provides a general strategy for the encapsulation of macromolecules in MS materials.