Bioactive flake-shell capsules: soft silica nanoparticles for efficient enzyme immobilization

Amorphous silica particles are used extensively in industrial processes as well as in scientific and biomedical research. Flake-shell silica nanoparticles, prepared by self-templating hydrothermal synthesis, exhibit large surface areas and pore volumes, hollow spherical morphology, as well as hydrophilic surfaces, affording great potential for their application in enzyme immobilization. In this work we show that the shell, which is composed of a network of silica flakes, promotes uptake of enzymes of different sizes, i.e., lysozyme, lipase, and chymotrypsin. Moreover, the capsules provide a favorable porous structure for diffusion of small substrate molecules while permitting enzymes to retain their activity. The silica composition of the capsules provides structural stability, biocompatibility and allows easy functionalization. Amine and dextran functionalities were introduced to modify the shell morphology and to control enzyme loading and activity. The efficient protein immobilization on these inorganic capsules should lead to their application in biocatalysis, biosensing and drug delivery.