Ion implantation treatment of beads for covalent binding of molecules: application to bioethanol production using thermophilic beta-glucosidase.

We have achieved plasma immersion ion implantation (PIII) treatment of beads and powders using a specially designed plasma treatment system. This simple one-step production of functionalized beads provides an attractive alternative to current commercial functional beads, for which proteins must be chemically attached using linkers. Using the enzyme beta-glucosidase as an example we show that PIII treatment of polyethylene beads enables covalent binding with increased activity of the enzyme compared to the untreated beads. Covalent binding was confirmed using detergent washing. The covalently immobilized enzyme has a broader pH range over which it has high activity than the enzyme in solution. The stability of the immobilized molecules was examined using reaction rate as a function of temperature and was shown to be significantly higher on the PIII treated beads compared to untreated beads. We attribute the increased enzyme activity on PIII treated beads to increased protein binding density and better retention of conformation. The results of this work are of significance in the production of ethanol using a flow process. Covalent binding to beads allows more robust attachment for high flow rates, high activity, large surface area and a broad operating pH range. Treatment could be easily adapted for a range of applications such as linking drugs, dyes and proteins to particles of an appropriate size.