The initial step of the natural photosynthetic process, the capture of light energy, is the main reason for the high efficiency found in photosynthesis. The absorption of light energy is performed by pigment-protein complexes called light harvesting antennae. In cyanobacteria and red algae, the major antenna is called the Phycobilisome (PBS), which transfers the absorbed energy to the photochemical reaction center with a quantum efficiency of nearly 100%. The unique PBS complex is made of small subunits, the most abundant of which is called Phycocyanin (PC).

In nature, these light harvesting molecules have evolved gradually over approximately 3 billion years, thus light harvesting proteins could be used as the inspiration for light harvesting elements in artificial photosynthesis or as energy transporting elements in bio-electronic devices.

Bio-electronics has the potential to significantly impact many areas of research including: medicine, environment, food engineering, alternative energy, and many others. In this study, we demonstrate that highly stable PC from the thermophilic cyanobacterium Thermosynechococcus vulcanus (Tv) presents an ideal candidate for investigation in bio-electronic devices.

In order to demonstrate this proposal, two types of systems were developed in order to investigate the Tv PC qualities and advantages; the first system developed is a self-assembled Tv PC super structure comprised of millions of Tv PC subunits which self-assemble into long wires used as a light guide.

We observed and analyzed the organization and formation of dehydrated Tv PC on inorganic materials into long wires using light and electron microscopy, and have successfully measured an energy transfer distance through the wire reaching up to 2μm using an NSOM technique. The second system is a bio-hybrid solar cell made from TiO2/Pt electrodes, similar to Grätzel Cell also known as the “dye-sensitized solar cell” (DSSC). In this system, we replaced the organic dye with Tv PC and measured the direct solar absorption to electricity conversion, using chronoamperometry, cyclic voltammetry, and incident photon to charge carrier conversion efficiency (IPCE).

The bio-hybrid solar cell showed poor efficiency of 0.0265% and Fill Factor (FF) of 0.387, but with a high performance of 4.37 mA/cm2 at 0.2 V, the highest current density of protein based solar cell ever reported. The results from this project provide evidence that thermophilic proteins such as Tv PC may serve as better candidates in future bio-electronic devices, and that the Tv PC especially holds great promise as an energy transporter and stable protein in such systems.