A New Surface for Immobilizing and Maintaining the Function of Enzymes in a Freeze-Dried State

We describe a new surface produced by plasma treatment for immobilizing proteins in the dry state. The need for surfaces suitable for immobilizing proteins is increasing because of demand for microarray diagnostic services, biosensors, and chemical processing. Storage of surface attached proteins in the dry state offers benefits of long shelf life, protection from proteases, easier transportation and convenient storage. In this work, we produced plasma-modified polyethylene surfaces and tested them using two important enzymes for which convenient functional assays are available, namely, horseradish peroxidase and catalase. Over 80% of the function of horseradish peroxidase is retained after freeze-drying, and this function is unaltered after 4 months of storage at 4 degrees C on the treated polyethylene surface. The factors important for maintenance of surface attached enzyme stability were (1) plasma immersion ion implantation (PIII) treatment of the surface, (2) freeze-drying with sucrose in the buffer solution, (3) dry storage with desiccant, and (4) maintaining the freeze-dried protein at a reduced temperature. Other than sucrose, no other additives are needed.