New bio-inorganic photo-electronic devices based on photosynthetic proteins

Abstract

Construction of efficient devices for light energy conversion, including photo-electronic and photovoltaic (PV) devices, is a big challenge for the current science and technology that will have important economic consequences. Most of the modern photovoltaic devices are based on silicon. An innovative approach to the construction of photovoltaic devices is the utilization of biological systems and principles designed for similar purposes by Nature. Biological electronic devices, proteins, have extremely high efficiency, precise spatial organization, and are inexpensive in fabrication. They can be fused with inorganic and organic materials such as conductors, semiconductors, conductive polymers, or quantum dots. The photosynthetic reaction center protein (RC) is one of the most advanced photo-electronic devices developed by Nature. It has nearly 100% quantum yield of primary charge separation, an extremely fast operation time (about 10^-9 s, or operation frequency of ~10⁹ Hz), and a very efficient stabilization of separated charges (ratio of charge separation rate to that of charge recombination is about 10⁴). The charge separation and stabilization takes place in a complex of 7 nm size and leads to the formation of a local electric field of about 10⁶ V/cm. A coupling of photosynthetic RC to inorganic electrodes is attractive for the identification of the mechanisms of inter-protein electron transfer (ET) and for the possible applications in the construction of protein-based innovative photoelectronic and photovoltaic devices. In this presentation we describe a new type of hybrid bio-inorganic photoelectronic devices based on photosynthetic proteins and inorganic materials. Using genetically engineered bacterial RCs and specifically synthesized organic linkers, we were able to construct self-assembled and aligned protein complexes with various metals and semiconductors, including gold, indium tin oxide (ITO), nanoporous TiO₂, highly ordered pyrolytic graphite (HOPG) and carbon nanotube (CNT) arrays. Our results show that photosynthetic protein-inorganic complexes can operate as highly efficient photo- and chemo-sensors, optical switches, photorectifieres, or photovoltaic devices.