Two-dimensional protein crystals for solar energy conversion

Ordered 2D light harvesting protein Photosystem I (PSI) crystals were used on a bilayer support with intercalated conjugated oligoelectrolyte (COE) units and measured photocurrents comparable with thick film devices. Self assembly was induced through dialysis to produce 2D PSI lipid crystals. PSI particles were precipitated using PEG6000/MgCl₂ and resuspended in 0.5% octyl-Β,D-thioglucoside (OTG), 10mM HEPES pH 7.0. The PSI was mixed with DMPC solubilized in 2% OTG using a LPR w/w of 0.4-1.0 and a final concentration of 1.0 mg/mL PSI. The detergent concentration of the reconstitution mixture was adjusted to 0.95% and dialyzed against detergent free buffer. Detergent free crystals were adsorbed on glow discharged carbon coated electron microscopy grids, stained with 0.75% uranyl formate, and imaged. The functional PSI crystals can be adsorbed onto a tBLM that has been treated with membrane-intercalating COE molecules. As a result of incorporating these COEs one observes that the photocurrent activity of the PSI crystals is 4-fold greater relative to unmodified tBLM layers and to previously studied PSI monolayers on self assembled monolayers (SAMs).