Modified structural and optical characteristics of Au-NPs-MWCNTs nanohybrids

Nanohybrids formed by the multiwalled carbon nanotubes (MWCNTs) and metallic nanoparticles (NPs) have gained immense interest recently for their potential biological applications. In this paper, we present a comprehensive study of the nanohybrid formed with varied concentrations of Au-NPs with MWCNTs. It is demonstrated that the concentration of Au-NPs in the nanohybrid is crucial in defining ultimate characteristics of the nanohybrid. The MWCNTs were functionalized with varied concentrations of Au-NPs (40-100 nano Molar (nM)) and characterized extensively by the X-ray diffraction, electron microscopy, Raman spectroscopy and UV-Vis absorption spectroscopy. The process of purification and acid treatment led to the activation of -COOH bond at the surface of MWCNTs and functionalization with Au-NPs also induced stresses as observed in the X-ray diffraction patterns. The fusion of Au-NPs in the MWCNTs was clearly observed in the high resolution TEM images, which affected the D and G - Raman bands of the MWCNTs significantly as studied by the line shape analysis. The Au-NPs-MWCNTs nanohybrids were then used to study the effect of various concentrations of E-coli using Raman spectroscopy and absorption spectroscopy. Due to intrinsic negative charge present on the E-coli, the local charge densities varied at the surface of MWCNTs as soon as it was covered with E-coli, and resulted in the shift of both G and D bands and increased intensity ratio of the two bands. The variation in the charge density in Au-NPs due to its binding with MWCNTs and adsorption of E-coli was reflected in the blue shift of the surface plasmon modes. Finally, it is concluded that ratio of Au-NPs and MWCNTs is crucial in forming nanohybrid for applications.