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Individual protein complex generates electric current

Solar cell consisting of a single molecule

Graphical image of a photosystem I-complex which is lit by the tip of a optical near-field microscope
Photosystem-I (green) is optically excited by an electrode (on top). An electron then is transferred step by step in only 16 nanoseconds. Image: Christoph Hohmann (NIM)

Research news

Photosynthesis allows plants to convert light into chemical energy. Utilizing this process to produce electrical energy is a research goal worldwide. Now a team of scientists at the Technische Universität München and the Tel Aviv University has succeeded in directly deriving and measuring the photoelectric current generated by single molecules of the photosystem I.

The scientist investigated the photosystem-I reaction center which is a chlorophyll protein complex located in membranes of chloroplasts from cyanobacteria. Plants, algae and bacteria use photosynthesis to convert solar energy into chemical energy. The initial stages of this process – where light is absorbed and energy and electrons are transferred – are mediated by photosynthetic proteins composed of chlorophyll and carotenoid complexes. Until now, none of the available methods were sensitive enough to measure photocurrents generated by a single protein. Photosystem-I exhibits outstanding optoelectronic properties found only in photosynthetic systems. The nanoscale dimension further makes the photosystem-I a promising unit for applications in molecular optoelectronics.

The first challenge the physicists had to master was the development of a method to electrically contact single molecules in strong optical fields. The central element of the realized nanodevice are photosynthetic proteins self-assembled and covalently bound to a gold electrode via cysteine mutation groups. The photocurrent was measured by means of a gold-covered glass tip employed in a scanning near-field optical microscopy set-up. The photosynthetic proteins are optically excited by a photon flux guided through the tetrahedral tip that at the same time provides the electrical contact. With this technique, the physicists were able to monitor the photocurrent generated in single protein units.

The research was supported by the German Research Foundation (DFG) via the SPP 1243 (grants HO 3324/2 and RE 2592/2), the Clusters of Excellence Munich-Centre for Advanced Photonics and Nanosystems Initiative Munich, as well as ERC Advanced Grant MolArt (no. 47299).

Original publication:

Photocurrent of a single photosynthetic protein
Daniel Gerster, Joachim Reichert, Hai Bi, Johannes V. Barth, Simone M. Kaniber, Alexander W. Holleitner, Iris Visoly-Fisher, Shlomi Sergani, and Itai Carmeli
nature nanotechnology, 30. Sept. 2012 – DOI: 10.1038/nnano.2012.165

Contact:

Dr. Joachim Reichert,
Technische Universität München
Physik-Department E20
James-Franck Strasse, D-85748 Garching, Germany
Tel.: +49 89 289 12443 – Fax:+49 89 289 12338
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Prof. Alexander W. Holleitner
Technische Universität München
Walter Schottky Institut – Zentrum für Nanotechnologie und Nanomaterialien
Am Coulombwall 4a, 85748 Garching, Germany
Tel.: +49 89 289 11575 – Fax: +49 89 289 12600
E-MailInternet

Dr. Itai Carmeli
Tel Aviv University
Center for NanoScience and Nanotechnology and School of Chemistry,
Tel Aviv 69978, Israel.
Tel.: +972-3-6405704 – Fax: +972-3-6405612
E-MailInternet