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The construction of efficient light energy converting (photovoltaic and photo-electronic)
devices is a current and great challenge in science and technology and one that will have
important economic consequences. Several innovative nanoelectronic materials were
proposed to achieve this goal, semiconductor quantum dots, metallic nanowires and
carbon nanotubes (CNT) are among them. As a charge separating unit for light energy
conversion, we propose the utilization of the most advanced photoelectronic material
developed by nature, photosynthetic reaction center proteins. As a first step in this
direction, we constructed a novel bioinorganic nanophotoelectronic material with
photoactive photosynthetic reaction center (RC) proteins encapsulated inside a multiwall
CNT arrayed electrode. The material consists of photosynthetic RC-cytochrome
complexes acting as charge separating units bound to the inner walls of a CNT electrode
and ubiquinone-10 (Q2) serving as a soluble electron-transfer mediator to the counter
electrode. The proteins were immobilized inside carbon nanotubes by a Ni(NTA)-alkane-pyrene
linker, forming a self-assembled monolayer (SAM) on the surface of inner CNT
walls and allowing for unidirectional protein orientation. The material demonstrates an
enhanced photoinduced electron transfer rate and shows substantial improvement in
photocurrent density compared to that obtained with the same proteins when immobilized
on planar graphite (HOPG) electrode. The results suggest that protein encapsulation in
precisely organized arrayed tubular electrode architecture can considerably improve the
performance of photovoltaic, photoelectronic, or biofuel cell devices. They demonstrate
the potential for substantial advantages of precisely organized nano electrode tubular
arrayed architecture for variety biotechnological applications.
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