There is now a method under development that can measure photocurrents of a single functionalized photosynthetic protein system which means a one molecule in a solar cell.
The scientists could demonstrate that such a system can integrate and address in artificial photovoltaic device architectures while retaining their biomolecular functional properties. The proteins represent light-driven, highly efficient single-molecule electron pumps that can act as current generators in nanoscale electric circuits.
A team of scientists conducting the research consists of Joachim Reichert, Johannes Barth, and Alexander Holleitner (Technische Universitaet Muenchen, Clusters of Excellence MAP and NIM), and Itai Carmeli (Tel Aviv University)
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 absorbs and energy and electrons transfer – end up 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. They measured the photocurrent by means of a gold-covered glass tip employed in a scanning near-field optical microscopy set-up.
The photosynthetic proteins end up 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.