Polarized Raman spectroscopy of aligned DNA-wrapped single-wall carbon nanotubes

Abstract

This study introduces a new method to create highly ordered, self-aligned arrays of single-wall carbon nanotubes (SWCNTs) using short DNA composed of 20 thymine bases, known as Poly(dT)20. The SWCNTs were first functionalized through a chemical treatment involving a mixture of sulfuric acid (H₂SO₄) and nitric acid (HNO₃) in a 3:1 ratio, followed by uniform dispersion achieved via a cold ultrasonic technique. Subsequently, the Poly(dT)20 was wrapped around the SWCNTs using a sonothermal process, with variations in time and temperature to enhance alignment. The structural integrity and alignment of the resulting Poly(dT)20 /SWCNT arrays were characterized using scanning electron microscopy (SEM), and profile meter geometry analysis, all of which confirmed the successful alignment of the SWCNTs. Further analysis through ultraviolet-visible spectroscopy (UV–VIS) and Fourier-transform infrared spectroscopy (FTIR) provided evidence of the bonding interactions between the Poly(dT)20 and SWCNTs. Ennhanced Raman spectroscopy of the Poly(dT)20/SWCNT arrays, conducted with polarized light, revealed a significant dependence of the G-band on the polarization angle, yielding a depolarization ratio of 0.211 and linear relationship between I and Cos ² (α). The HRTEM image confirms that the attachment of 20-mer thymine to single-walled carbon nanotubes (SWCNTs) by wrapping around them introduces steric hindrance, which physically separates the nanotubes and prevents aggregation. This finding indicates a well alignment of the Poly(dT)20/SWCNT arrays. The anisotropic characteristics exhibited by the SWCNTs in conjunction with the Poly(dT)20 as a biomaterials suggest promising applications in various fields, including biomedical components, nano-electronic devices, and bio-optics.