Uniform and monodispersed silica nanoparticles were synthesized with a mean diameter of 100 +/- 20 nm as analyzed by Transmission Electron Microscopy (TEM). Glutaraldehyde was used as a coupling agent for efficient binding of the lipase onto the silica nanoparticles. For the hydrolysis of pNPP at pH 7.2, the activation energy within 25-40 degrees C for free and immobilized lipase was 7.8 and 1.25 KJ/mol, respectively. The V(max) and K(m) of immobilized lipase at 25 degrees C for pNPP hydrolysis were found to be 212 mu mol/min/mg and 0.3 mM, whereas those for free lipase were 26.17 mu mol/min and 1.427 mM, respectively. The lower activation energy of immobilized lipase in comparison to free lipase suggests a change in conformation of the enzyme leading to a requirement for lower energy on the surface of the nanoparticles. A better yield (7 fold higher) of ethyl isovalerate was observed using lipase immobilized onto silica nanoparticles in comparison to free lipase. (C) 2008 Elsevier Ltd. All rights reserved.