Template-synthesized nanotubes for biotechnology and biomedical applications

Spherically shaped micro- and nano-particles are typically used for drug deliver, but this only reflects the fact that spheres are easier to make than other shapes. Micro and nanotubes, structures that resemble tiny drinking straws, are alternatives to spherical nanoparticles. Examples include organosilicon polymer nanotubes, self-assembling lipid microtubes, fullerene carbon nanotubes, template-synthesized nanotubes, and peptide nanotubes. Nanotubes offer some interesting advantages relative to spherical nanoparticles for biotechnological applications. For example, nanotubes have large inner volumes (relative to the dimensions of the tube), which can be filled with any desired chemical or biochemical species ranging in size from proteins to small molecules. In addition, nanotubes have distinct inner and outer surfaces, which can be differentially chemically or biochemically functionalized. This creates the possibility, for example, of loading the inside of a nanotube with a particular biochemical payload but imparting chemical features to the outer surface that render it biocompatible. Finally, nanotubes have open mouths, which makes the inner surface accessible and incorporation of species within the tubes particularly easy. We review here template synthesis method for preparing micro and nanotubes, and we give examples of recent biotech applications of these tubular systems. This review is not intended to be all encompassing; instead it discusses recent trends and emphasizes template synthesis method.