Raman spectroscopy of networking of carbon nanotubes wrapped with single- or double-stranded DNA or surrounded by N-methylpyrrolidone molecules: Region of D and G modes

The Raman spectra of single-walled carbon nanotubes (SWNTs) wrapped with single-stranded (ssDNA) or double-stranded DNA (dsDNA), as well as those surrounded by N-methyl-2-pyrrolidone (NMP) molecules, were analyzed in the region corresponding to the tangential (G) and defect-induced (D) modes (1200–1700 cm–1). Nanotubes were sprayed from aqueous (with DNA) or NMP suspensions on quartz substrates, forming a network. From atomic force microscopy images follow that the networking is formed by individual nanotubes and small bundles. The spectra showed noticeable differences between the samples, reflecting variations in the structural organization of the DNA wrapped around nanotubes and the features of the interaction of NMP with nanotubes. Small spectral differences of D-band are observed between ssDNA- and dsDNA-wrapped SWNTs networking, although broader G– and G+ bands in SWNTs:dsDNA samples indicate the presence of small bundles, likely due to the weaker binding efficiency of dsDNA with the nanotube compared to ssDNA. In contrast, the D-band in the SWNTs:NMP sample is approximately twice as intense, broader, and shifted towards lower frequency by 2 cm–1 compared to the D-band in the spectrum of DNA-wrapped SWNTs, indicating stronger defect-related scattering. The G+ peak positions remain nearly unchanged across all samples, while this band in the SWNTs:NMP spectrum is significantly broader. The G–-bands in the spectrum of DNA-wrapped SWNTs and SWNTs:NMP differ in intensity and position, reflecting distinct interactions between the nanotube and surrounding. The influence of a combination of factors, such as bundling, charge transfer, stress induced by adsorbed molecules, and changing dielectric constants due to different surroundings on the shift of the band peak, the increase in intensity, and the broadening of bands in the Raman spectrum of SWNTs is discussed.