Physical adsorption of proteins on to inorganic supports such as zeolites and silica is a well-documented phenomenon. We utilized enzyme immobilization in halloysite nanotubes by loading anionic proteins inside of halloysite's 15nm lumen.  This can be accomplish efficiently because: 1) The diameter of the lumen is large enough to accommodate proteins of 2-5nm diameter and the hydrophilic chemical character of said lumen. 2) Since the interior of the tube is positively charged and the exterior is negatively charged, one can prevent adsorption of protein on the outer surface of the tube by controlling the pH relative to the proteins pI. We have demonstrated loading of various proteins, with a net negative charge in water, such as glucose oxidase, pepsin, urease, and lipase. We were able to load the proteins into the nanotubes from concentrated aqueous solutions and achieve 5-8 wt % loading efficiency, dry them for long term storage while preserving moisture inside of the tubes, then utilize the sample for release kinetic studies or enzymatic activity assays. Approximately 25% of the loaded protein was released within five to six hours after being place into solution, while the other half seem resistant leaving the lumen of halloysite.  Halloysite nanotubes are non-toxic and biocompatible and if loaded with biologically active materials then one can imagine the many potential uses of these functionalized nanocontainers.

Natural clay nanotubes as a novel enzyme immobilization support

247th National Meeting (2014)

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