Single-walled carbon nanotubes (SWNTs) have unique
photophysical properties but low fluorescence efficiency. We
have found significant increases in the fluorescence efficiency of
individual DNA-wrapped SWNTs upon addition of reducing agents,
including dithiothreitol, Trolox, and β-mercaptoethanol. Brightening
was reversible upon removal of the reducing molecules, suggesting
that a transient reduction of defect sites on the SWNT sidewall causes
the effect. These results imply that SWNTs are intrinsically bright
emitters and that their poor emission arises from defective nanotubes.