Photoelectric Monolayers Based on Self-Assembled and Oriented Purple Membrane Patches

The fabrication of dry ultrathin photoelectric layers is described in this paper. The self-assembled monolayer of oriented purple membrane (PM) patches from bacteriorhodopsin (bR) is created on a bio-functionalized gold (Au) surface using a biotin molecular recognition technique. The biotin enables the extracellular side of the bR PMs to be accurately labeled. During the biochemical immobilization process, the biotinylated alkylthiols modify the Au surface using HS terminals of the thiols and affix the labeled bR to the functionalized surface using streptavidin-biotin interactions. An optically transparent indium tin oxide (ITO) electrode is then placed on top of the finished assembly to complete the circuit of the photocell for testing and performance verification. An experimental study shows that the proposed self-assembly method can produce a 12.33 nm thick photoelectric layer that generates nearly 0.54 mV/(mW ·cm²) when exposed to a 568-nm laser beam. In contrast, other immobilization techniques such as electric field sedimentation produce dry bR films that are more than 10 μm thick. These ultrathin photoelectric layers can be used to create nanoscale light sensors and photocells.