Enzyme multilayers on colloid particles:: Assembly, stability, and enzymatic activity

Colloidal biocatalysts, comprising polystyrene (PS) carrier particles coated with enzyme multilayers, were fabricated via the layer-by-layer self-assembly method. Glucose oxidase (GOD), horseradish peroxidase (POD), or preformed enzyme-polyelectrolyte complexes were assembled in alternation with oppositely charged polyelectrolytes onto PS particles. Microelectrophoresis, single-particle light scattering, and transmission electron microscopy confirmed stepwise growth of the multilayer films on the colloid particles. The high surface area Enzyme multilayer-coated particles were successfully employed as specific enzyme reactors (i.e., as catalysts). Whereas no loss in activity was observed for the enzymes immobilized directly onto particle surfaces, precomplexing the enzymes with polymer in solution drastically reduced their activity (by up to 70%). The enzymatic activity (per particle) was found to increase with the number of enzyme layers immobilized, irrespective of whether the enzyme was precomplexed. However, particles coated with preformed enzyme-polyelectrolyte complexes displayed a significantly lower enzymatic activity than those fabricated by the direct adsorption of free enzyme. Multicomponent films of GOD and POD on colloid particles were also prepared, and sequential enzymatic catalysis was demonstrated. Furthermore, experiments were conducted with particles exhibiting both magnetic and catalytic functions. These particles, premodified with a layer of magnetic nanoparticles to impart a magnetic property and subsequently coated with enzyme multilayers, were repeatedly used as catalysts following their rapid and easy separation with a magnet. Such biocolloids are expected to find applications in biotechnology.