Synthesis of Nickel−Nitrilotriacetic Acid Coupled Single-Walled Carbon Nanotubes for Directed Self-Assembly with Polyhistidine-Tagged Proteins

Nickel−nitrilotriacetic acid-functionalized single-walled carbon nanotubes have been synthesized for the directed, reversible self-assembly of polyhistidine-tagged macromolecules onto the nanotube surface. Carbon nanotubes were first covalently functionalized with 4-carboxybenzene diazonium salt, which rendered them water-soluble. The acid moieties on the carbon nanotube were covalently reacted with N α, N α -bis(carboxymethyl)- l -lysine hydrate, forming amide bonds to the nanotube complex. The nitrilotriacetic acid (NTA) moiety of the N α, N α -bis(carboxymethyl)- l -lysine was complexed with Ni 2+ and used to specifically bind a polyhistidine-tagged photosynthetic reaction center (RC) from Rhodobacter sphaeroides as a model system. We demonstrate that the histidine-tagged RC protein (RC-His) specifically binds to SWNT-NTA-Ni in a reversible manner. The free RC-His in solution can be removed through histidine binding to Ni-NTA-agarose resin and purified by filtration. This approach allows for both positional and orientational control over protein binding to carbon nanotubes.