Studies of Hybrid Nano-Bio-System: Single-Walled Carbon Nanotubes and Hydrogenase

We have examined changes in single-walled carbon nanotube's (SWNTs) optical signals upon addition of [FeFe] hydrogenases (H2ase). Evidence was found that stable SWNT/H2ase charge-transfer complexes self-assemble in solution under conditions of H₂ase catalytic turnover. Raman studies suggest that metallic SWNT can undergo either forward or reverse electron transfer depending on the H2ase redox state. This amphoteric behavior is due to the electronic band structure of the metallic SWNTs, which leads to both occupied and empty mid-gap electron states at the Fermi level. In contrast, semiconducting SWNT, which had no mid-gap states, can only accept electrons from the reduced H₂ase. In context of hybrid SWNT-H₂ase based devices, metallic SWNTs are more suited for applications as a conductive molecular wire, while semiconducting SWNTs are more suited for use in nanoscale sensors or photovoltaic devices.