Intercalating purple membranes into 2D β-alanine crystals to enhance photoelectric and nonlinear optical properties

Versatile Protein-A Coated Photoelectric Immunosensors with a Purple-Membrane Monolayer Transducer Fabricated by Affinity-Immobilization on a Graphene-Oxide Complexed Linker and by Shear Flow

“…The surface area covered only by single b-PM monolayers increased from 21% to 91% after the slow washing procedure. Further close-up topographic analysis of those b-PM monolayers revealed most of them no longer looked slightly elliptical, and had fused with neighboring monolayers and hence become larger in size (Figure 3(b-V)), suggesting the occurrence of dynamic transitions and redistribution of b-PM monolayers during the washing step, similar to our previous observations [7,10]. Examining the interior membrane structures in the close-up images of those flow-treated b-PM surfaces revealed the initial cracked structure in the bottom layer in Figure 3(b-I,b-II,b-IV), which was identified as the CP side of PM [33], no longer appeared in Figure 3(b-V), indicating reorganization of b-PM monolayers during the flow-assisted fusion process.…”

“…BR is the only protein component in the purple membrane (PM) of Halobacterium salinarum , natively existing in a trimeric form hexagonally packed as a highly compact and stable two-dimensional (2D) crystalline structure resistant to extreme pHs and temperatures [8]. Each BR monomer contains a retinal chromophore conjugated with Lys216, which isomerizes from the all- trans to the 13- cis conformation upon illumination, pumping protons unidirectionally from the cytoplasmic (CP) to the extracellular (EC) side of PM and consequently generating a photovoltaic force as well as an electrical impulse through the external circuit [7,8,9,10]. On the premise the bacterial cells captured close to PM block part of the incident light and thus reduce BR photocurrents, the previous BR-based immunosensor was constructed for the first time by anchoring cell-specific biotinylated antibodies through NeutrAvidin, a deglycosylated form of avidin, on the PM patches that had been unidirectionally immobilized on an electrode and then surface-conjugated with biotin on their exposed CP side [7].…”