Name: self-assembly of hybrid lipid membranes doped with hydrophobic organic molecules at the water/air interface
Uploaded: 2020-05-01T14:00:00
Description: Watch this Scientific Journal Video about Self-Assembly of Hybrid Lipid Membranes Doped with Hydrophobic Organic Molecules at the Water/Air Interface at JoVE.com

This work was supported by the CREST program of the Japan Science and Technology Agency (JPMJCR14F3) and Grant in-Aids from Japan Society for the Promotion of Science (19H00846 and 18K14120). This work was partly carried out at the Laboratory for Nanoelectronics and Spintronics, Research Institute of Electrical Communication, Tohoku University.

1. Preparation of a hybrid solution
<ol>
	<li>Wash four 4 mL disposable glass vials and screw caps (with PTFE coated seals) in an ultrasonic bath for 10 min in distilled water (purified with a filtration system), followed by ethanol and chloroform, respectively. Dry the glass vials and caps in a stream of nitrogen gas.</li>
	<li>In an anaerobic glove box, prepare a CuPc stock solution (10 mg/mL) in a washed glass vial by dissolving powdered CuPc in chloroform.</li>
	<li>Filter the CuPc solution through a 0.2 &#181;m po...

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In the precursor solution of the hybrid membrane, a mixed organic solvent (chloroform and hexane) rather than pure chloroform is used to dissolve lipids and CuPc. If pure chloroform is used, the density of the precursor solution would be higher than water. Therefore, it is highly likely that the solution would sink to the bottom of water rather than spread on water surface. Adding hexane, a low density solvent, to the precursor solution, ensures that the solution will float on the water surface and form a uniform hybrid ...

As essential frameworks of cell membranes, the interior of cells are separated from the exterior by a lipid bilayer system. This system consists of amphiphilic phospholipids, which are composed of hydrophilic phosphoric ester &#8220;heads&#8221; and hydrophobic fatty acids &#8220;tails&#8221;. Due to remarkable fluidity and self-assembly ability of lipid bilayers in aqueous environment1,2, artificial lipid bilayers can be formed using simple methods3,4. Various types of membrane proteins, such as ion channels, membrane receptors and enzymes, have been incorporated into the artificial lipid bilayer to mimic and study the functions of cell membranes5,6. More recently, lipid bilayers have been doped with nanomaterials (e.g., metal nanoparticles, graphene, and carbon nanotubes) to form functional hybrid membranes7,8,9,10,11,12,13. A widely used method for forming such hybrid membranes involves the formation of doped lipid vesicles, which contain hydrophobic materials such as modified Au-nanoparticles7 or carbon nanotubes11, and the resulting vesicles are then fused into planar supported lipid bilayers. However, this approach is complex and time-consuming, which limits the potential uses of such hybrid membranes.
In this work, lipid membranes were doped with organic molecules to produce hybrid lipid membranes that formed at the water/air interface by self-assembly. This protocol involves three steps: preparation of the mixed solution, formation of a hybrid membrane at the water/air interface, and the transfer of the membrane onto a Si substrate. Compared with other previously reported methods, the method described here is simpler and does not require sophisticated instrumentation. Using this method, air-stable hybrid lipid membranes with a larger area can be formed in a shorter time. The nanomaterial used in this study is a semiconducting organic molecule, copper (II) 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (CuPc), which is widely used in a number of applications, including solar cells, photodetectors, gas sensors and catalysis14,15. CuPc, a small organic molecule with a planar structure, has a high affinity for the &#8220;tails&#8221; of phospholipids duo to its hydrophobic characteristics. Other groups have reported that CuPc molecules can self-assemble on single-crystal surfaces with the formation of highly ordered structures16,17. Therefore, it is highly possible that the CuPc molecules could be incorporated into the lipid bilayers through self-assembly.
We provide a detailed description of the procedures used to form membranes and provide some suggestions for smoothly implementing this procedure. In addition, we present some presentative results of the hybrid lipid membranes, and discuss potential applications of this method.

<table>
	<tbody>
		<tr>
			<td>Chloroform</td>
			<td>Wako&#160;Chemicals</td>
			<td>033-08631</td>
			<td></td>
		</tr>
		<tr>
			<td>CuPc</td>
			<td>Sigma-Aldrich</td>
			<td>423165</td>
			<td></td>
		</tr>
		<tr>
			<td>DPhPc</td>
			<td>Avanti Polar Lipids</td>
			<td>850356C</td>
			<td></td>
		</tr>
		<tr>
			<td>Glass vials with screw cap</td>
			<td>Nichiden-Rike Glass Co., Ltd</td>
			<td>6-29801</td>
			<td></td>
		</tr>
		<tr>
			<td>Hexane</td>
			<td>Wako&#160;Chemicals</td>
			<td>084-03421</td>
			<td></td>
		</tr>
		<tr>
			<td>Membrane filters</td>
			<td>Merck Millipore Ltd.</td>
			<td>R8CA42836</td>
			<td></td>
		</tr>
		<tr>
			<td>Micro-syringe</td>
			<td>Hamilton</td>
			<td>80530</td>
			<td></td>
		</tr>
		<tr>
			<td>Peristaltic pump</td>
			<td>Tokyo Rikakikai Co., Ltd.</td>
			<td>11914199</td>
			<td></td>
		</tr>
		<tr>
			<td>Vortex mixer</td>
			<td>Scientific Industries, Inc.</td>
			<td>SI-0286</td>
			<td></td>
		</tr>
	</tbody>
</table>

self-assembly of hybrid lipid membranes doped with hydrophobic organic molecules at the water/air interface

Because of their unique properties, including an ultrathin thickness (3-4 nm), ultrahigh resistivity, fluidity and self-assembly ability, lipid bilayers can be readily functionalized and have been used in various applications such as bio-sensors and bio-devices. In this study, we introduced a planar organic molecule: copper (II) 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (CuPc) to dope lipid membranes. The CuPc/lipid hybrid membrane forms at the water/air interface by self-assembly. In this membrane, the hydrophobic CuPc molecules are located between the hydrophobic tails of lipid molecules, forming a lipid/CuPc/lipid sandwich structure. Interestingly, an air-stable hybrid lipid bilayer can be readily formed by transferring the hybrid membrane onto a Si substrate. We report a straightforward method for incorporating nanomaterials into a lipid bilayer system, which represents a new methodology for the fabrication of biosensors and biodevices.

The as-formed membrane has a uniform light blue color due to the presence of CuPc molecules. The area of the colored membrane is normally several square centimeters. In Figure 1A and Figure 1B, we show a microscopic image and an atomic force microscope (AFM) image (including a height profile) of the hybrid lipid membrane on a Si substrate. In the AFM image, the membrane in the upper left is thick, with a thickness of 79.4 nm and that at the lower right is thin, ...

Watch this Scientific Journal Video about Self-Assembly of Hybrid Lipid Membranes Doped with Hydrophobic Organic Molecules at the Water/Air Interface at JoVE.com

Self-Assembly of Hybrid Lipid Membranes Doped with Hydrophobic Organic Molecules at the Water/Air Interface

We report a protocol for producing a hybrid lipid membrane at the water/air interface by doping the lipid bilayer with copper (II) 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (CuPc) molecules. The resulting hybrid lipid membrane has a lipid/CuPc/lipid sandwich structure. This protocol can also be applied to the formation of other functional nanomaterials.

Because of their unique properties, including an ultrathin thickness (3-4 nm), ultrahigh resistivity, fluidity and self-assembly ability, lipid bilayers ...

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