Visualizing the local optical response of semiconducting carbon nanotubes to DNA-wrapping,” Nano Lett

We studied the local optical response of semiconducting single-walled carbon nanotubes to wrapping by DNA segments using high resolution tip-enhanced near-field microscopy. Photoluminescence (PL) near-field images of single nanotubes reveal large DNA-wrapping-induced red shifts of the exciton energy that are two times higher than indicated by spatially averaging confocal microscopy. Near-field PL spectra taken along nanotubes feature two distinct PL bands resulting from DNA-wrapped and unwrapped nanotube segments. The transition between the two energy levels occurs on a length scale smaller than our spatial resolution of about 15 nm. Semiconducting single-walled carbon nanotubes (SWNTs) as photoluminescent quasi-one-dimensional systems have attracted enormous scientific interest and have large potential for various applications in photonics and opto- and nano-electronics.1-3 Photoluminescence (PL) of nanotubes results from exciton recombination and occurs in the near-infrared spectral range with emission energies controlled mainly by the nanotube structure (n,m).4-8 Since nanotubes consist of surface atoms only, the detected emission energy is ver