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Description
Rei Furukawa1 Shunsuke Yajima2 Masaharu Kondo2 Kenji Nagashima3 Morio Nagata4 Takehisa Dewa2 Mamoru Nango5

1, University of Electro-Communications, Tokyo, , Japan
2, Nagoya Institute of Technology, Nagoya, Aichi, Japan
3, Kanagawa University, Hiratsuka, Kanagawa, Japan
4, Tokyo University of Science, Tokyo, Tokyo, Japan
5, Osaka City University, Osaka, Osaka, Japan

BACKGROUND
(photosynthetic proteins and its highly efficent energy harvesting)


Nano-scale patterns of LH (light-harvesting) pigment-protein complexes in a photosynthetic membrane are known to capture photons that is followed by an highly efficient excitation energy transfer[Ke, Photosynthesis]. A typical photosynthetic membrane takes a configuration of LH2 complexes surrounding LH1-RC (reaction center) complexes. In this distribution, excitation energy transfer from LH2 to LH1-RC are known to be accomplished in a high efficiency. One way to reveal how this protein distribution is contributing the excellent photon-electron conversion is to compare the photovoltaic signal from the actual co-assembled system of LH1-RC and LH2 in different distributing patterns.

WHAT WE HAVE DONE
(patterning of two LH proteins and its photoelectric measurement)


We have prepared a co-immobilized LH1-RC and LH2 on a common substrate. Isolation and immobilization methods of each proteins are described in our previous reports [Yajima, Appl. Phys. Lett. 2012] [Kondo, Biomacromol., 2012]

Using this sample substrate, photoelectric signal was observed using different illuminating wavelengths that each correspond to the excitations of LH1 and LH2 pigments.

As a result, enhancement of photocurrent was observed from LH1-RC with the co-existence of adjacent LH2. In addition, enhancement was as well observed using LH2 excitation wavelength compared to the case using LH1 exciting wavelength. The result indicates that the rearranged organization of LH complexes onto an inorganic substrate was successful in exhibiting the characteristic of natural photosynthetic membrane.

The work is expected to be useful in providing guidelines for materials design for organic/inorganic solar cells as well as its contribution for photosynthetic study field.

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