Fusion of purple membranes triggered by immobilization on carbon nanomembranes

René Riedel,Daniel Rhinow,Norbert Hampp,Martin Wortmann,Raphael Dalpke,Natalie Frese,Fang Yang,Armin Gölzhäuser

doi:10.3762/bjnano.12.8

Abstract

A freestanding ultrathin hybrid membrane was synthesized comprising two functional layers, that is, first, a carbon nanomembrane (CNM) produced by electron irradiation-induced cross-linking of a self-assembled monolayer (SAM) of 4′-nitro-1,1′-biphenyl-4-thiol (NBPT) and second, purple membrane (PM) containing genetically modified bacteriorhodopsin (BR) carrying a C-terminal His-tag. The NBPT-CNM was further modified to carry nitrilotriacetic acid (NTA) terminal groups for the interaction with the His-tagged PMs forming a quasi-monolayer of His-tagged PM on top of the CNM-NTA. The formation of the Ni-NTA/His-tag complex leads to the unidirectional orientation of PM on the CNM substrate. Electrophoretic sedimentation was employed to optimize the surface coverage and to close gaps between the PM patches. This procedure for the immobilization of oriented dense PM facilitates the spontaneous fusion of individual PM patches, forming larger membrane areas. This is, to our knowledge, the very first procedure described to induce the oriented fusion of PM on a solid support. The resulting hybrid membrane has a potential application as a light-driven two-dimensional proton-pumping membrane, for instance, for light-driven seawater desalination as envisioned soon after the discovery of PM.

Highlights

The so-called purple membrane (PM) has attracted large attention in the scientific literature after this light-driven proton pump was first discovered in the 1970s [1,2]
The carbon nanomembrane (CNM) substrates were prepared by deposition of 60 μL wild-type PM (WT PM) suspension in distilled water with different optical densities (OD) for 20 min on the NBPT CNM substrate
A proof of concept has been demonstrated for the fabrication of a large-area hybrid nanoscale membrane of unidirectionally oriented and, at least partially, fused PM patches on a functionalized NBPT CNM substrate

Summary

Introduction

The so-called purple membrane (PM) has attracted large attention in the scientific literature after this light-driven proton pump was first discovered in the 1970s [1,2]. We report the successful assembly of a unidirectionally oriented PM quasi-monolayer on an ultrathin carbon nanomembrane (CNM) substrate. Preliminary experiments were performed to obtain both optimal orientations of the PM patches and coverage of the CNM substrate.

Results

Conclusion