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Photocurrent of a single photosynthetic protein

Abstract

Photosynthesis is used by plants, algae and bacteria to convert solar energy into stable chemical energy. The initial stages of this process—where light is absorbed and energy and electrons are transferred—are mediated by reaction centres composed of chlorophyll and carotenoid complexes1. It has been previously shown that single small molecules can be used as functional components in electric2,3,4,5,6 and optoelectronic circuits7,8,9,10, but it has proved difficult to control and probe individual molecules for photovoltaic11,12,13 and photoelectrochemical applications14,15,16. Here, we show that the photocurrent generated by a single photosynthetic protein—photosystem I—can be measured using a scanning near-field optical microscope set-up. One side of the protein is anchored to a gold surface that acts as an electrode, and the other is contacted by a gold-covered glass tip. The tip functions as both counter electrode and light source. A photocurrent of 10 pA is recorded from the covalently bound single-protein junctions, which is in agreement with the internal electron transfer times of photosystem I.

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Figure 1: Measuring the photocurrent of a single PS I.
Figure 2: The reaction-centre electron transfer chain, showing electron transfer and recombination times.
Figure 3: Current versus gap distance profiles.
Figure 4: Photocurrent analysis and histograms.

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Acknowledgements

This work was supported by the DFG via SPP 1243 (grants HO 3324/2 and RE 2592/2), COST-Phototech, the China Scholarship Council, the Nanosystems Initiative Munich (NIM), the Munich Center for Advanced Photonics (MAP), ERC Advanced Grant MolArt (no. 47299) and the Center of NanoScience (CeNS) in Munich. The authors thank A. Brenneis for technical assistance.

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Authors and Affiliations

Authors

Contributions

D.G. and H.B. performed the experiments and analysed the data. I.C. produced the PS I mutants and self-assembly techniques, and introduced the theory. A.W.H. supervised sample preparation. J.R. supervised the photocurrent experiments. S.M.K. prepared the PS I substrates. I.C., I.V.F., A.W.H. and S.S. performed preliminary atomic force microscopy and scanning tunnelling microscopy measurements. J.R. and I.C. conceived the study and co-wrote the paper with A.W.H., J.V.B. and I.V.F.

Corresponding authors

Correspondence to Joachim Reichert or Itai Carmeli.

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The authors declare no competing financial interests.

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Gerster, D., Reichert, J., Bi, H. et al. Photocurrent of a single photosynthetic protein. Nature Nanotech 7, 673–676 (2012). https://doi.org/10.1038/nnano.2012.165

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