Engineering Photosystem I Complexes for use in Bio-Hybrid Dye-Sensitized Solar Cells

Increasing global population, growing per capita energy needs, diminishing fossil fuels, and climate change collectively will require new, innovative, and sustainable alternatives to meet the world’s growing energy needs. One of the most promising yet simple approaches are dye-sensitized solar cells (DSSCs). However, conventional DSSCs use semi-conductor anodes sensitized with complex synthetic organometallic dyes. Most dyes utilize ruthenium complexes to absorb photons, which upon excitation, inject electrons into the anode, while holes migrate to the cathode via liquid electrolyte. However, these dyes are expensive, difficult to make, and resource-limited. This dissertation focuses on replacing synthetic dyes with the naturally occurring, biological pigment-protein complex photosystem I (PSI). Using synthetic biology we have engineered PSI subunits (PsaD and PsaE) along with ferredoxin to bind to metal-oxides using metal-oxide binding peptides (MOBiP). Specifically, we have produced ZnO binding peptides (ZOBiP) fused PSI subunits (PsaD and PsaE) and TiO2 binding peptides (TOBiP) fused ferredoxin (Fd). Recombinantly produced ZOBiP-PsaD/E and TOBiP-Fd have been characterized via Western blotting, CD, and MALDI-TOF. The ZOBiP-PSI subunits have been used to replace wild-type PsaD/E at efficiencies up to 90%, and TOBiP-Fd has been cross-linked to PSI. These MOBiP-PSI complexes have been produced and incubated with various metal-oxide nanoparticles, showing a selectivity in binding. We will take advantage of this to create efficient MOBiP-PSI DSSCs. Photocurrent has been generated by MOBiP-PSI complexes. Surface area of the DSSCs is being increased by the inclusion of ZnO and TiO2 nanowires. Constructs are being made to produce these MOBiP-PSI complexes in vivo using two different species of cyanobacteria (Syn 6803 and T.e.).