Silaffin polypeptides from diatoms catalyze the biomineralization of silica in vitro, thereby entrapping the peptides during the generation of the silica matrix. This observation led us to explore the use of the biomimetic silicification reaction for the entrapment of exogenously added enzyme in a silica matrix. The versatility of the silica-immobilization method has now been investigated for a variety of biomolecules with consistently high immobilization efficiencies and retention of enzyme activity. Enzyme immobilization stabilizes the labile nature of biomolecules and facilitates substrate and product recovery, prevents product contamination and in certain instances, improves the properties of the biocatalyst. The silica-enzyme nanocomposites exhibit excellent mechanical stability and provide a versatile and effective method for developing immobilized enzyme reactors, applicable to biocatalysis, biosensors and drug discovery.