Recent advances in the development of functionalized carbon nanotubes: a versatile vector for drug delivery

Carbon nanotubes (CNTs) possess unique physical and chemical properties and can serve as a platform for transporting a variety of bioactive molecules, such as drugs, proteins, and genes, given appropriate surface modifications. Here, we present an overview of the progress in applying CNTs as therapeutic agent carriers. Drugs can be attached to CNTs either through supramolecular chemistry to form noncovalent assembly or via covalent linkage to the functional groups preinstalled on CNTs. In addition to surface loading, packing of molecules inside the internal cavity of CNTs to protect less stable entities has also been achieved. Besides drugs, the high specific surface area of CNTs can also allow the installation of multiple molecules with different functions, e.g. target recognition and optical imaging, simultaneously to achieve synergistic effects. The drug release process tends to be gradual and sustained after being attached to CNTs, and could be tuned by various factors, such as pH, diameter of CNTs, and target recognition. The content throughout this review is mainly focused on the different protocols of loading drugs onto or into CNTs as well as how to control the drug release.