Peptide cross-linking modulated stability and assembly of peptide-wrapped single-walled carbon nanotubes

Carbon nanotubes have interesting electronic, optical and mechanical properties that are potentially useful for diverse applications—from nanoscale electronic devices to super tough fibers, super capacitors and artificial muscles. However, carbon nanotubes are difficult to solubilize for processing into needed architectures. In previous studies, we demonstrated that the designed amphiphilic α-helical peptide nano-1 can non-covalently attach to the surface of single-walled nanotubes (SWNTs) and increase SWNT solubilization in aqueous solution. To improve both the efficiency of nano-1 solubilization of SWNTs and the stability of nano-1/SWNT composites, we now evaluate the use of 1-ethyl-3-[3-dimethylaminopropyl]carbodiimide hydrochloride (EDC) to cross-link nano-1 peptides to each other around SWNTs by forming amide bonds between the side chains of Lys and Glu amino acids. We find that cross-linking nano-1/SWNT dispersions increases the solubilization capacity of HiPco SWNTs in aqueous solution. Furthermore, the stability of the peptide/SWNT dispersions towards dilution by water is significantly enhanced. Finally, when dried the cross-linked nano-1/SWNT dispersions self-assemble into extended fiber-like structures containing aligned nanotubes.