Such carbonyls may be further oxidized using potassium permanganate (KMnO4) and per- chloric acid (HClO4) to convert all of these groups into carboxylic acids. Once functionalized in this manner, the nanotubes can be fully dispersed in aqueous systems. Kordás et al. (2006) used these derivatives to print nanotube patterns on paper or polymer surfaces to create con- ductive patterns for potential use in electronic circuitry. The carboxylates also may be used as conjugation sites to link other ligands or proteins to the nanotube surface using a carbodiimide reaction as previously discussed (Section 1, this chapter; Chapter 2, Section 1.11; Chapter 3, Section 1).