Nanotube-Peptide Interactions on a Silicon Chip

Using the tools of modern molecular biology, we probe the interaction of nanotubes on silicon chips with proteins via combinatorial phage display methods. By screening against a large library of random peptides, we find that over half of the single-walled carbon nanotube (SWNT)-binding peptides show a motif of SXWWXXW, where S is serine, W is tryptophan, and X is anything. In a helical wheel diagram, this peptide is amphiphilic, where the hydrophobic and aromatic tryptophan side groups are concentrated on one face of an alpha-helix. This theme is robust and occurs in all of the SWNT-binding peptides. Surprisingly, the other aromatic amino acids seem less likely to show up in the screen, indicating a special role of tryptophan in binding to SWNTs. By elucidating the physical principles underlying the interaction between SWNTs and peptides and proteins, this work lays the foundation for the eventual human (or computer) nanoengineered, precise, and economical manipulation of nanotubes using peptides and proteins for nanotube sorting, assembly into electronic components, and understanding the effect of biological function.