Double-stranded (ds) DNA of a λ-phage virus are combed on octadecyltrichlorosilane (OTS)-modified borosilicate glass substrates and investigated by means of tip-enhanced Raman spectroscopy (TERS) using tips coated with an Ag/Au bilayer. Owing to an enhancement factor higher than 6 × 10 2 and a lateral spatial resolution better than 9 nm (which is below the size of the tip apex radius), cross-sections of nanowire-shaped thin DNA bundles can be spatially resolved. TER spectra reveal vibrational modes typical of DNA nucleobases and backbone, as confirmed by confocal Raman measurements carried out on dense stacks of DNA strands. While the TER signature of nucleobases is congruent with observations in single-stranded (ss) DNA, additional modes tied to the DNA backbone can be discerned in ds DNA. TERS enables ss and ds DNA samples to be distinguished from each other and hence can be exploited for the detection of DNA hybridization. Moreover, no TER contribution of the OTS layer appears, suggesting that functionalized DNA strands could be studied without spectral perturbation from the substrate. This work paves the way toward the nanoscale spectral study of organized DNA-based nanostructures.

Raman-active vibrational modes of (6,5) chirality-enriched single-walled carbon nanotubes (SWNTs), helically wrapped by semiconducting poly[2,6-{1,5-bis(3-propoxysulfonic acid sodium salt)}naphthylene]ethynylene (PNES), are described in great detail. At an irradiation wavelength of 568.2 nm, the extent to which the environment impacts the nanotube vibrational signature can be probed; in particular, the absence of a G band shift for PNES–[(6,5) SWNT] samples relative to benchmark surfactant-coated nanotubes indicates the lack of any significant charge transfer between the PNES strand and the SWNT skeleton, but electronic spectra provide compelling evidence for polymer-to-SWNT energy transfer. At an irradiation wavelength of 457.9 nm, vibrational modes associated with PNES chains that wrap (6,5) SWNTs are conspicuously enhanced. Under 514.5 nm irradiation, PNES–[(6,5) SWNTs] are not excited in resonance but G and G′ bands associated with these nanohybrids are strongly enhanced, reflecting the excitation of a multiphonon-mediated vibronic transition of the (6,5) SWNT backbone. At a 488.0 nm irradiation wavelength, Raman spectral signatures of both the PNES polymer and the vibronically excited (6,5) SWNT skeleton through one-phonon-assisted processes are pronounced, demonstrating that a specific SWNT chirality and the corresponding semiconducting polymer helically wrapped about its surface can be probed using an excitation wavelength that does not resonantly excite the SWNT structure.

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