Enzyme Loading in Internally-Coated Capillary Tubes via Kinetic Doping

Development of capillary tubes internally doped with enzymes is of great interest for microfluidic reactions, and kinetic doping could provide a facile, inexpensive method for their manufacture. Kinetic doping has previously been demonstrated to have a high loading capacity with thin films coated on flat-surface coverslips. Dip coating of these surfaces was developed with the eventual intention to coat different shapes and sizes of substrates. In this study, we expanded the use of kinetic doping to internally-coated capillary tubes. Parameters for internally doping capillary tubes were developed with rhodamine 6G, which produced internally-coated thin films with a 90 nm thickness. Horseradish peroxidase (HRP) was then loaded into the capillary tubes, with a 47,000x increase in concentration over the loading solution. After excluding surface-adsorbed protein, the increase in HRP concentration in the thin films over the loading solution was determined to be 9850x. The activity of the loaded HRP was determined to be 0.019 +/- 0.003 U/mg and shown to have a stronger resistance to denaturation by methanol.