Photocurrents Generated by Bacteriorhodopsin Adsorbed on Nano-Black Lipid Membranes

Abstract

Purple membranes were adsorbed on freestanding lipid bilayers, termed nano-black lipid membranes (nano-BLMs), suspending the pores of porous alumina substrates with average pore diameters of 280 nm. Nano-BLMs were obtained by first coating the upper surface of the highly ordered porous alumina substrates with a thin gold layer followed by chemisorption of 1,2-dipalmitoyl-sn-glycero-3-phosphothioethanol and subsequent addition of a droplet of 1,2-diphytanoyl-sn-glycero-3-phosphocholine and octadecylamine dissolved in n-decane onto the hydrophobic submonolayer. By means of impedance spectroscopy, the quality of the nano-BLMs was verified. The electrical parameters confirm the formation of single lipid bilayers with high membrane resistances covering the porous matrix. Adsorption of purple membranes on the nano-BLMs was followed by recording the photocurrents generated by bacteriorhodopsin upon continuous light illumination. The membrane system exhibits a very high long-term stability with the advantage that not only transient but also stationary currents are recordable. By adding the proton ionophore carbonyl cyanide-m-chlorophenylhydrazone the conductivity of the nano-BLMs increases, resulting in a higher stationary current, which proves that proton conductance occurs across the nano-BLMs.

Nano for bio: Nanopore arrays for stable and functional lipid bilayer membranes (Mini Review)

“…[42][43][44][45][46] The formation of bilayers was confirmed by electrochemical impedance spectroscopy ͑EIS͒ analysis. An adequate equivalent circuit model is a prerequisite for fitting the measured data points aimed at providing resistance and capacitance values of the membrane.…”

4 Electrochemistry of Biomimetic Membranes

“…These nano-BLMs were also used to record the photocurrents generated by purple membrane fragments adsorbed on the lipid bilayers spanning the micropores. 112 Purple membranes from Halobacterium salinarium are very rich in the proton pump bacteriorhodopsin, which pumps protons from the cytoplasmic to the extracellular side of the bacterium membrane upon photoactivation by green light. The purple membrane fragments were added to the compartment exposing the gold-coated side of the alumina membrane.…”

Investigating cellular electroporation using planar membrane models and miniaturized devices

“…with a large number of apertures), as shown in figure 3.12B. The pores (size < 100 μm [118]) are created in a silicon substrate by a photolithography step, followed by an anodization process whereas for the alumina substrates only an anodization process is employed and pores are much smaller (< 300 nm [118][119][120][121][122]). Furthermore, as before, a layer of insulating silicon oxide is added onto the silicon substrate by thermal oxidation.…”

“…The size of the microapertures is strongly dependent on the material in which the aperture is machined and on the fabrication technique. Nanometer-sized apertures are reported for silicon, silicon nitride and porous alumina substrates [107,113,[118][119][120][121][122], whereas in glass and polymer-based devices the apertures mainly remain in the micrometer range. Similarly, the seal resistance is affected by the nature of the material, and does not only depend on the size of the aperture.…”

“…In some devices, protein insertion is followed by studies that are more complex. Examples of those are the effects of the binding of chemicals to proteins, such as β-cyclodextrins, DNA or ATP (Adenosine triphosphate) [85,[107][108]122] and the recording of the photocurrent generated by bacteriorhodopsin upon illumination [120]. Besides, in some of the systems the membranes are now positioned horizontally, allowing for the optical detection of the membrane surface area [115].…”