Single-walled carbon nanotubes form the basis of new non-photobleaching cell markers that remain visible in live cells for up to three months and do not impede cell viability. In-vitro spectroscopy of the intrinsic near-IR fluorescence and Raman scattering of the nanotubes maps the localization of nanotube complexes, which accumulate in perinuclear endosomes (see Figure). The markers are also detectable in hematoxylin and eosin stained cells and exhibit spectral changes due to the nanotubes' environment.