Solar Cell Made of a Single Molecule: Electrical Current Generated from Individual Protein Complex

 
A method to measure the photocurrents of a ‘single functionalized photosynthetic protein system’ has now been developed by researchers. The researchers are confident that they can show that such a system could be integrated and “selectively addressed” inside of an artificial photovoltaic device’s architecture while still being able to retain its “biomolecular functional properties.”

The protein is essentially a light-driven and highly efficient single-molecule electron pump, a pump that can potentially act as a power generator in nanoscale electric circuits.

The researchers were investigating the photosystem-I reaction center — that’s a chlorophyll protein complex that is located in the membranes of chloroplasts from cyanobacteria. Photosynthesis is used by algae, plants, and some bacteria in order to convert the Sun’s energy into usable and storable 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 this breakthrough, there weren’t any methods that were sensitive enough to measure the photocurrents that are 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 primary challenge to the physicists was that they had to develop and master “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,” a Technische Universitaet Muenchen news release states. ”

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.” Using this technique allowed the researchers to monitor the photocurrent being generated in single protein units.

The research team is publishing the results of the research in the journal Nature Nanotechnology this week.

The research was the result of interdisciplinary cooperation between researchers, led by Joachim Reichert, Johannes Barth, and Alexander Holleitner (Technische Universitaet Muenchen, Clusters of Excellence MAP, and NIM), and Itai Carmeli (Tel Aviv University)

Source: Technische Universitaet Muenchen
Image Credits: Christoph Hohmann (NIM)