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 degrees C. After being stored for 30 days at 4 degrees C, the immobilized enzyme had 75% of the initial activity. The maximum apparent Michaelis constant for free urease (K-m) was 94.33 mM whereas for immobilized urease was 53.04 mM. The maximum reaction velocity (V-max) for free urease was 3.51 mmol/min and for immobilized urease was 1.57 mmol/min. (c) 2006 Elsevier Ltd. All rights reserved.