Highly hydrophilic and stable polypeptide/single-wall carbon nanotube conjugates

Abstract

A polymeric dispersing agent for single-wall carbon nanotubes (SWCNTs) in water was synthesized by 4-(pyren-1-yl)butanoylation of the amine groups of poly-L-lysine. The pyrene content of 4-(pyren-1-yl)butanoylated polylysine (PBPL) was optimized so that a maximal dispersion effect of the SWCNTs was obtained. High molecular weight PBPL (>300000 g mol⁻¹) exceeds the widely used surfactant sodium dodecylsulfate (SDS) as a dispersing agent yielding a 27% higher SWCNT concentration in dispersion. The high stability of the PBPL/SWCNT conjugates is demonstrated by removing the conjugates from dispersion through filtration, washing, and redispersion in only water. The resulting redispersions do not contain free PBPL and the importance of having SWCNT dispersions in the absence of free dispersing agent is discussed. For SDS dispersions, poor redispersion properties have been observed. The binding of PBPL onto the SWCNTs was studied by atomic force microscopy, optical absorbance spectroscopy, and fluorescence spectroscopy.