Wiring-Up Hydrogenase with
Single-Walled Carbon Nanotubes
Timothy J. McDonald,Drazenka Svedruzic,Yong-Hyun Kim,Jeffrey L. Blackburn,
S. B. Zhang,Paul W. King,* andMichael J. Heben*
Energy Sciences, National Renewable Energy Laboratory, Golden, Colorado 80401
Received September 10, 2007
Abstract:
Many envision a future where hydrogen is the centerpiece of a sustainable, carbon-free energy supply. For example, the energy in sunlight
may be stored by splitting water into H2 and O2 using inorganic semiconductors and photoelectrochemical approaches1 or with artificial
photosynthetic systems that seek to mimic the light absorption, energy transfer, electron transfer, and redox catalysis that occurs in green
plants.2 Unfortunately, large scale deployment of artificial water-splitting technologies may be impeded by the need for the large amounts of
precious metals required to catalyze the multielectron water-splitting reactions. Nature provides a variety of microbes that can activate the
dihydrogen bond through the catalytic activity of [NiFe] and [FeFe] hydrogenases,3,4 and photobiological approaches to water splitting have
been advanced.5 One may also consider a biohybrid approach; however, it is difficult to interface these sensitive6, 7 metalloenzymes to other
materials and systems. Here we show that surfactant-suspended carbon single-walled nanotubes (SWNTs) spontaneously self-assemble with
[FeFe] hydrogenases in solution to form catalytically active biohybrids. Photoluminescence excitation and Raman spectroscopy studies show
that SWNTs act as molecular wires to make electrical contact to the biocatalytic region of hydrogenase. Hydrogenase mediates electron
injection into nanotubes having appropriately positioned lowest occupied molecular orbital levels when the H2 partial pressure is varied. The
hydrogenase is strongly attached to the SWNTs, so mass transport effects are eliminated and the absolute potential of the electronic levels
of the nanotubes can be unambiguously measured. Our findings reveal new nanotube physics and represent the first example of "wiring-up"
an hydrogenase with another nanoscale material. This latter advance offers a nonprecious metal route to the design of new biohybrid architectures
and building blocks for hydrogen-related technologies.
