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Photocurrent generation by direct electron transfer using photosynthetic reaction centres

Publication Type:

Journal Article


SMART MATERIALS \& STRUCTURES, Volume 20, Number 9, SI (2011)


Photosynthetic reaction centres (RCs) convert light into separated
charges with nearly perfect quantum efficiency, and have been used to
generate photocurrent. Previous work has shown that electron tunnelling
rates between redox centres in proteins depend exponentially on the
tunnelling distance. In this work the RC from Rhodobacter sphaeroides
was genetically modified with the aim of achieving the shortest
tunnelling distances yet demonstrated between the RC's
electron-accepting P site and underlying graphite and gold electrodes,
and between the electron donor Q site and graphite electrodes. Opposite
charges are carried to counter electrodes using mobile mediators, as in
dye-sensitised solar cells. Native RCs are bound to graphite surfaces
through N-(1-pyrene) iodoacetamide. Although the linker's length is only
4 angstrom, the electron transfer pathway between the Q electron donor
site on the RC and the electrode surface is still too large for current
to be significant. A mutant version with the electron acceptor P side
close to the graphite surface produced currents of 15 nA cm(-2) upon
illumination. Direct binding of RCs to a gold surface is shown,
resulting in currents of 5 nA cm(-2). In both cases the current was
unaffected by mediator concentration but increased with illumination,
suggesting that direct electron transfer was achieved. The engineering
of an RC to achieve direct electron transfer will help with long term
efforts to demonstrate RC-based photovoltaic devices.