Credit: © 2007 ACS

Hydrogenase enzymes, which are found in various microbes, can catalyse the reversible oxidation of molecular hydrogen, providing a biological alternative to expensive precious-metal catalysts. There has, therefore, been great interest in their potential for use in biofuel cells and hydrogen production. However, it is difficult to incorporate them into electrical devices without compromising their catalytic activity.

Now, a group from the National Renewable Energy Laboratory in Colorado in the US have made biohybrids from hydrogenases and single-walled carbon nanotubes (SWNTs) in which the nanotube acts as a molecular wire and forms an electrical connection to the catalytic region of the hydrogenase. Michael J. Heben and colleagues1 used an iron-based hydrogenase from the bacterium Clostridium acetobutylicum and simply mixed it with a suspension of SWNTs in a surfactant. The enzyme spontaneously displaced the surfactant and adsorbed onto the SWNT surfaces.

Photoluminescence excitation and Raman spectroscopy studies were used to evaluate electron transfer in the hybrid material. Under anaerobic conditions and with an appropriate H2 partial pressure, the hydrogenase remained catalytically active and could mediate the injection of electrons into the nanotube.