It has been 9 years (!) since the report of solubilization of single-walled carbon nanotubes (SWNTs) by Robert Haddon and coworkers (Jian Chen, et al., "Solution Properties of Single-Walled Carbon Nanotoubes", Science 1998, 282, 95).
This first report established the fact that the heavily bundled SWNTs can be made floating around in solution - more than the state of "suspension" - by attaching "soluble hooks" (functional groups) to the nanotubes.
The bonding was based on amide linkage between the amino groups of the functionl group, octadecylamine (ODA), and the nanotube surface-bound carboxylic acids, which are from the oxidized sp3 carbons (ends and defects) and could be easily generated via chewing the tubes with some oxidative acid (refluxing in diluted nitric acid for 24h will do). Because these carboxylic acids are outcasts (located at ends and mostly pre-existing defects), namely, not interfering with the overal nanotube structure, the SWNT electronic properties are largely preserved after such functionalization (later refered to as defect-targeted functionalization).
The solvents were organic, due to the lipophilic nature of the soluble functional groups. Apparently, when the functional groups become hydrophilic, the nanotubes will be water-soluble.
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