Carbon nanotubes can be functionalized via amidation and esterification of the nanotube-bound carboxylic acids. The solubility of these functionalized carbon nanotubes makes it possible to characterize and study the properties of carbon nanotubes using solution-based techniques. Representative results concerning the solubility, dispersion, defunctionalization, and optical properties of the functionalized carbon nanotubes are presented. Several examples for the use of functionalized carbon nanotubes in the fabrication of polymeric carbon nanocomposites, the probing of nanotube-molecule interactions, and the conjugation with biological species are highlighted and discussed.

Carbon nanotubes are functionalized by bovine serum albumin (BSA) proteins via diimide-activated amidation under ambient conditions. The nanotube-BSA conjugates thus obtained are highly water-soluble, forming dark-colored aqueous solutions. Results from characterizations using atomic force microscopy (AFM), thermal gravimetric analysis, Raman, and gel electrophoresis show that the conjugate samples indeed contain both carbon nanotubes and BSA proteins and that the protein species are intimately associated with the nanotubes. Bioactivities of the nanotube-bound proteins are evaluated using the total protein micro-determination assay (the modified Lowry procedure). The results show that the overwhelming majority (∼90%) of the protein species in the nanotube-BSA conjugates remain bioactive.

Lipophilic and hydrophilic dendra which are terminated with long alkyl chains and oligomeric poly(ethylene glycol) moieties, respectively, were synthesized, and these dendron species were used to functionalize single-wall (SWNT) and multiple-wall (MWNT) carbon nanotubes via amidation and esterification reactions. The functionalized carbon nanotube samples are, depending on the functionalities, soluble in common organic solvents, such as hexane and chloroform, and water to form colored homogeneous solutions. Characterizations using NMR, electron microscopy, and optical spectroscopic techniques show that the homogeneous solutions contain carbon nanotubes. A preliminary understanding of the structural features and properties of these soluble dendron-functionalized SWNTs and MWNTs is discussed in terms of results from the characterizations, the defunctionalization reactions, and the trapping of metal nanoparticles by the functionalized nanotubes in solution.

Unique properties of PGA, and its modifications and applications.