Using a Light-Driven Proton Pump Protein to Develop a Reduction-Oxidation Reaction Cell

Abstract

Bacteriorhodopsin (BR) is a membrane protein found in the halophilic archaea Halobacterium salinarum, which is characterized as a light-driven proton pump. BR has a wide range of absorption wavelength in visible light, high thermal stability and a broad range of pH tolerability, which render the possibility of using it for bioelectronic applications. Here, we developed a novel device utilizing BR as a photoactive agent to generate steady currents through the continuous reduction-oxidation reaction of proton under light illumination. We inserted BRs originally protected by detergents into liposomes by dialysis and used the charges of liposomes and pH to control the insertion orientation of BR into the liposomes in order to increase the later proton pumping efficiency. We deposited the liposomes with BRs on a porous support to form a supported lipid bilayer (SLB) with BRs. This porous support-SLB-BR structure, which separated platinum cathode from anode, allowed the BRs to pump proton and accumulate electrical potential in a specific direction in response to sunlight. The differences of the proton concentration and electrical potential across the porous support-SLB-BR structure could drive the reduction-oxidation reaction at the electrodes, and therefore generated an electrical current.