Modifying the sidewalls of single-walled carbon nanotubes can affect the optical and electronic properties of the tubes. Covalent reactions have been used to join different chemical groups to the sidewalls of nanotubes but these reactions randomly erode the ordered π-electron structure and suppress the near-infrared fluorescence signature peaks of the tubes. Bruce Weisman and colleagues at Rice University have now shown that introducing a low concentration of oxygen atoms to single-walled carbon nanotubes can systematically change their optical properties for better detection.
To prepare the oxygen-doped nanotubes, Weisman and colleagues exposed an aqueous suspension of pristine, semiconducting single-walled carbon nanotubes to low doses of ozone followed by light. Fluorescence spectroscopy showed that treated samples had distinct near-infrared fluorescence at longer wavelengths than pristine tubes, and Resonance Raman spectroscopy confirmed the presence of covalently bonded oxygen in the treated samples. The red-shifted emission, which is absent in pristine nanotubes, meant that the doped nanotubes were more readily detected in cultured cells than pristine tubes.
The method offers a simple way to systematically shift the optical properties of pristine nanotubes to achieve better fluorophores for imaging.