Supramolecular Chemistry on Water-Soluble Carbon Nanotubes for Drug Loading and Delivery

We show that large surface areas exist for supramolecular chemistry\non single-walled carbon nanotubes (SWNTs) prefunctionalized noncovalently\nor covalently by common surfactant or acid-oxidation routes. Water-soluble\nSWNTs with poly(ethylene glycol) (PEG) functionalization via these routes allow for surprisingly high degrees of π-stacking\nof aromatic molecules, including a cancer drug (doxorubicin) with\nultrahigh loading capacity, a widely used fluorescence molecule (fluorescein),\nand combinations of molecules. Binding of molecules to nanotubes and\ntheir release can be controlled by varying the pH. The strength of\nπ-stacking of aromatic molecules is dependent on nanotube diameter,\nleading to a method for controlling the release rate of molecules\nfrom SWNTs by using nanotube materials with suitable diameter. This\nwork introduces the concept of “functionalization partitioning”\nof SWNTs, i.e., imparting multiple chemical species,\nsuch as PEG, drugs, and fluorescent tags, with different functionalities\nonto the surface of the same nanotube. Such chemical partitioning\nshould open up new opportunities in chemical, biological, and medical\napplications of novel nanomaterials.