A hollow cathode glow discharge was used to functionalize single-wall carbon nanotubes. This low temperature, solvent free, facile and fast process may be used to efficiently attach various functional groups (COOH, OH, CH, NH(2), NO(2) and NO) to the open ends and sidewalls of carbon nanotubes. The presented technique yields a broader set of functional groups being attached to the tubes as compared to other discharge routes. A rich functionalized surface provides an attractive scaffold for the further coupling of complex molecules, e.g., enzymes, antibodies. In situ optical emission spectroscopy investigations provided detailed information of the dynamic processes within the plasma itself. The findings show a gas temperature of 480 K and suggest the functionalization occurs through radical addition channels that are assisted by N(2) (+) radical ion collisions viz. N(2) (+) ion radical bombardment breaks C-C bonds on SWNTs surface opening a path for subsequent addition and quenching for other radical species.