Bacteriorhodopsin‐Monolayer‐Based Planar Metal–Insulator–Metal Junctions via Biomimetic Vesicle Fusion: Preparation, Characterization, and Bio‐optoelectronic Characteristics

A reliable and reproducible method for preparing bacteriorhodopsin (bR)‐containing metal–biomolecule–monolayer‐metal planar junctions via vesicle fusion tactics and soft deposition of Au top electrodes is reported. Optimum monolayer and junction preparations, including contact effects, are discussed. The electron‐transport characteristics of bR‐containing membranes are studied systematically by incorporating native bR or artificial bR pigments derived from synthetic retinal analogues, into single solid‐supported lipid bilayers. Current–voltage (I–V) measurements at ambient conditions show that a single layer of such bR‐containing artificial lipid bilayers pass current in solid electrode/bilayer/solid electrode structures. The current is passed only if retinal or its analogue is present in the protein. Furthermore, the preparations show photoconductivity as long as the retinal can isomerize following light absorption. Optical characterization suggests that the junction photocurrents might be associated with a photochemically induced M‐like intermediate of bR. I–V measurements along with theoretical estimates reveal that electron transfer through the protein is over four orders of magnitude more efficient than what would be estimated for direct tunneling through 5 nm of water‐free peptides. Our results furthermore suggest that the light‐driven proton‐pumping activity of the sandwiched solid‐state bR monolayer contributes negligibly to the steady‐state light currents that are observed, and that the orientation of bR does not significantly affect the observed I–V characteristics.