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Protein Nanopore Membranes Prepared by a Simple Langmuir-Schaefer Approach

Year: 2021

Journal: Small, Volume 17, NOV

Authors: Schwieters, Magnus S.; Mathieu-Gaedke, Maria; Westphal, Michael; Dalpke, Raphael; Dirksen, Maxim; Qi, Daizong; Grull, Marco; Bick, Thomas; Tassler, Stephanie; Sauer, Daniel F.; Bonn, Mischa; Wendler, Petra; Hellweg, Thomas; Beyer, Andre; Goelzhaeuser, Armin; Schwaneberg, Ulrich; Glebe, Ulrich; Boeker, Alexander

Organizations: Bundesministerium fur Bildung und Forschung (BMBF) [031B0559]; Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany's Excellence Strategy [EXC 2008 - 390540038 - UniSysCat]; Projekt DEAL

Keywords: glutaraldehyde; ion permeability; Langmuir technique; transmembrane proteins; ultrathin membranes; water permeance

Filtration through membranes with nanopores is typically associated with high transmembrane pressures and high energy consumption. This problem can be addressed by reducing the respective membrane thickness. Here, a simple procedure is described to prepare ultrathin membranes based on protein nanopores, which exhibit excellent water permeance, two orders of magnitude superior to comparable, industrially applied membranes. Furthermore, incorporation of either closed or open protein nanopores allows tailoring the membrane's ion permeability. To form such membranes, the transmembrane protein ferric hydroxamate uptake protein component A (FhuA) or its open-pore variant are assembled at the air-water interface of a Langmuir trough, compressed to a dense film, crosslinked by glutaraldehyde, and transferred to various support materials. This approach allows to prepare monolayer or multilayer membranes with a very high density of protein nanopores. Freestanding membranes covering holes up to 5 mu m in diameter are visualized by atomic force microscopy (AFM), helium ion microscopy, and transmission electron microscopy. AFM PeakForce quantitative nanomechanical property mapping (PeakForce QNM) demonstrates remarkable mechanical stability and elastic properties of freestanding monolayer membranes with a thickness of only 5 nm. The new protein membrane can pave the way to energy-efficient nanofiltration.