Bio-catalytic nanoparticles with urease immobilized in multilayer assembled through layer-by-layer technique

A novel core-shell colloid with multilayer for biocatalysis was elaborated by the layer-by-layer assembly technique. Urease was adsorbed in alternation with the oppositely charged polyelectrolytes onto polystyrene (PS) colloid nanoparticles as either polycation or polyanion switched by the solution pH. Microelectrophoresis, transmission electron microscopy (TEM) and UV-vis spectrum absorbance were employed to monitor the regular and stepwise growth of the multilayer films with the enzyme and counterpart polyelectrolytes. The colloid nanoparticles coated with negatively charged urease were found to be more stable than those coated with positively charged urease. The catalytic activity of the urease immobilized on the PS nanoparticles, having higher storage stability, was 23.67% of that for the free urease in aqueous solution. Addition of 0.05 M NaCl increased the activity of the immobilized urease by 65%. Coverage of synthetic polyelectrolyte layers on the urease layer reduced the activity of the immobilized urease. Therefore, by adding salts or covering with polyelectrolytes, we have achieved an enhancement or restraint of the bioactivity of immobilized enzyme, indicating a novel method for biotechnology.