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.

Decomposable hollow capsules based on deoxyribonucleic acid (DNA) and a low molecular weight organic molecule, a naturally occurring polyamine, spermidine (SP), were formed by applying the layer-by-layer adsorption strategy to colloid particles, viz., assembling DNA/SP multilayers on colloids and subsequently removing the templated core. For comparison, hollow capsules from the higher molecular weight biopolymers, alginate (ALG) and poly(lysine) (PL), were also prepared. The multilayers were first formed on polystyrene spheres, and their growth was followed by microelectrophoresis. The preparation of hollow capsules, derived from multilayer coating melamine formaldehyde core particles and then decomposing the core by acid treatment, was verified by atomic force microscopy and transmission electron microscopy. In contrast to the hollow ALG/PL capsules, the hollow DNA/SP capsules displayed a high sensitivity to salt solutions: Decomposition of the DNA/SP multilayers occurred after exposure to sodium chloride solutions. The hollow capsules prepared are attractive for the encapsulation and release of various substances; for example, the release of encapsulated compounds, such as dyes or drugs, can occur when loaded DNA/SP capsules are exposed to environmental (salt) conditions that decompose them, e.g., in the bloodstream.

Core-shell particles consisting of a polystyrene (PS) latex colloidal core and Fe(II) metallosupramolecular polyelectrolyte (Fe(II)-MEPE)/poly(styrenesulfonate) (PSS) multilayer shells were fabricated by the consecutive assembly of Fe(II)-MEPE and PSS on PS particles. The layers were deposited under conditions where the Fe(II)-MEPE and PSS are oppositely charged, thereby utilizing electrostatic attractions for multilayer buildup. Formation of Fe(II)-MEPE/PSS multilayers on weakly cross-linked melamine-formaldehyde (MF) particles, followed by MF particle decomposition and removal, resulted in hollow Fe(II)-MEPE/PSS shells. The Fe(II)-MEPE/PSS multilayer shell on the colloidal particles and the Fe(II)-MEPE/PSS hollow shells were found to be stable, resisting decomposition upon exposure to acidic solutions or chelating agents. PS latices as small as 70 nm in diameter were also employed as templates for the successful fabrication of Fe(II)-MEPE/PSS and poly(allylamine hydrochloride)/PSS multilayer shells. These results demonstrate that our approach can be extended to colloidal templates with diameters less than 100 nm. This work represents a first study of structurally well-defined metallo-supramolecular polyelectrolytecolloid assembles combining the functional units from supramolecular chemistry with the restricted dimensionality of colloids.

The construction of enzyme multilayer films on colloidal particles for biocatalysis is described. The enzyme multilayers were assembled on submicrometer‐sized polystyrene spheres via the alternate adsorption of poly(ethyleneimine) and glucose oxidase using a layer‐by‐layer approach. Microelectrophoresis and single particle light scattering measurements revealed regular and step‐wise assembly of the multilayers on the colloids. The high surface area bio‐multilayer coated particles formed were subsequently utilized in enzymatic catalysis.