Optical imaging is one of the most important techniques in biomedical studies. Recently, usage of near-infrared light has been extensively tried because of the higher transparency in biomaterials than the visible light. Single-walled carbon nanotubes (SWCNTs) are nanocarbon materials that show optical absorption and fluorescence in the near infrared (NIR) wavelength region. Especially, due to the bright fluorescence in NIR, SWCNTs have been expected as imaging probes.
In this talk, we first review the optical properties of SWCNTs and then show our recent results about the bio-application of oxygen-doped SWCNTs.1,2 Interestingly, covalent doping of the nanotube surface with a low concentration of oxygen atoms can create a new optically allowed defect state.3 Consequently, nanotube fluorescence is red-shifted and can be over 10 times brighter. Fluorescence vascular angiography and observation of the intestinal contractile activity of mice are demonstrated by using the produced oxygen-doped SWCNTs as infrared fluorescent labels and imaging agents.1 Further, the biodistribution analysis after the administration of the oxygen-doped SWCNTs in mice is also discussed by the resonance Raman spectroscopy and NIR fluorescence microscopy.2
 Y. Iizumi, M. Yudasaka, J. Kim, H. Sakakita, T. Takeuchi, T. Okazaki, Sci. Rep., 8, 6272 (2018).
 T. Takeuchi, Y. Iizumi, M. Yudasaka, S. Kondoh, T. Okazaki, in preparation.
 S. Ghosh, S. M. Bachilo, R. A. Simonette, K. M. Beckingham, R. B. Weisman, Science 330, 1656-1659 (2010).