Position-controlled vertical growths of individual carbon nanotubes using a cage-shaped protein

A novel biological path for position-controlled vertical growth of individual carbon nanotubes (CNTs) is presented. Catalysts of iron oxide nanoparticles (NPs, φ7nm) for CNT growth were synthesized homogeneously using a cage-shaped protein, apoferritin. Optimized electrostatic interaction between the protein cage and a substrate was used to position the apoferritin containing the NP core (called ferritin) one by one on a substrate. After the protein cages were eliminated, the NPs were left on the substrate preserving their adsorbed positions, thereby forming CNT growth points. Vertical CNT growths from each arranged NP were successfully achieved by plasma-enhanced chemical vapor deposition.