Immobilization of urease on vapour phase stain etched porous silicon

Porous silicon layers fabricated by the reaction-induced vapor phase stain etch method were coated with 5% polyethylenimine. Urease from Canavalia brasiliensis beans was immobilized on this support through covalent linking with 2.5% glutaraldehyde. The pH and temperature profile of the immobilized and free urease exhibited higher activity at pH 6.5 and 37 °C. After being stored for 30 days at 4 °C, the immobilized enzyme had 75% of the initial activity. The maximum apparent Michaelis constant for free urease (Km) was 94.33 mM whereas for immobilized urease was 53.04 mM. The maximum reaction velocity (Vmax) for free urease was 3.51 mmol/min and for immobilized urease was 1.57 mmol/min.