Immobilization of Proteins into Microcapsules and Their Adsorption Properties with Respect to Precious-Metal Ions

Abstract

We report on protein immobilization in a microcapsule and its adsorption performance with respect to precious-metal ions. Proteins including lysozyme, bovine serum albumin, chicken egg albumin, and soybean protein were immobilized by a microencapsulation method, and their adsorption properties with respect to ions of both precious metals (gold, platinum, and palladium) and base metals (zinc and copper) were investigated under various preparation conditions. Immobilized proteins could selectively adsorb precious-metal ions over base-metal ions. High immobilization efficiencies were obtained using lysozyme and soybean protein. The immobilization efficiency of the proteins was controlled by the surfactant concentration in the organic phase, the protein concentration, and the outer-aqueous-phase composition. We succeeded in immobilizing over 90% of the protein in the protein dose by optimizing the preparation conditions. Furthermore, the precious-metal ions adsorbed by the immobilized proteins were completely recovered with thiourea. No leakage of proteins was observed after the adsorption and desorption experiments. These results indicate that the microcapsules immobilizing proteins prepared in the present study can be used as reusable precious-metal-selective absorbents.