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...

<ol>
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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 ...

Our protocol demonstrate a simple method to fabricate organic molecule doped hybrid lipid membranes. The air stable property of the membrane can extend the application of lipid bilayer structure to solid state devices. We use a self-assembly process to form hybrid lipid membranes with a thickness of several nanometers.This protocol is simple and easy to follow and doesn't require complicated equipment. This method can be used to fabricate other same biohybrid lipid membranes and can be readily adopted to both sensors and other sensing devices. Working in an anaerobic glove box, dissolve copper phthalocyanine in chloroform inside a washed glass vial to prepare a 10 milligram per milliliter copper phthalocyanine stock solution.Filter the solution through a 0.2 micrometer PTFE membrane. Mix the DPHPC solution with a vortex mixer at 2, 300 RPM for 10 seconds. Then rinse a glass micro-syringe with chloroform five times and use it to transfer 200 microliters of the solution into a pre-washed glass vial.Evaporate the solvent in the vial with a gentle stream of nitrogen. Rinse another glass micro-syringe with chloroform, then use it to add 200, 2.6 microliters of chloroform to the glass vial with DPHPC. Add 47.4 microliters of the filtered copper phthalocyanine stock solution into the DPHPC solution which should result in a molar ratio of 10 to one DPHPC to phthalocyanine.Use another clean syringe to add 250 microliters of hexane to the solution. Then mix it with a vortex mixer at 2, 300 RPM for 10 seconds. Filter the prepared solution through a 0.2 micrometer PTFE membrane.Cut three by three centimeter silicon substrates from a silicon wafer. Then clean them in an ultrasonic bath for 10 minutes in purified water, followed by ethanol, and then chloroform. Treat the substrates with oxygen plasma for five minutes to remove adsorbed organic materials from the surface and to improve hydrophilicity.Wash a PTFE beaker with flowing purified water for three minutes. Then put the cleaned silicon substrate in the beaker tilted with a small angle. Pour a sufficient amount of purified water into the beaker until the entire silicon substrate is submerged.Take the prepared hybrid solution out of the freezer and allow it to warm to room temperature. Then stir it with a vortex mixer at 2, 300 RPM for 15 seconds. Use a rinsed 50 microliter micro-syringe to drop three to five microliters of the hybrid solution onto the water surface forming a floating hybrid lipid membrane.To transfer the membrane onto the silicon substrate, evaporate the organic solvent and pump the water out of the beaker with a peristaltic pump at a rate of three milliliters per minute. After the transfer process is complete, place the silicon substrate on a clean room wiper and allow all residual water to evaporate. The as formed hybrid lipid membrane has a uniform light blue color due to the presence of copper phthalocyanine molecules, and an area of several square centimeters.Shown here are confocal microscopy images and atomic force microscopy images of the membrane on a silicon substrate. In the AFM image, the membrane in the upper left is thick with a thickness of 79.4 nanometers, and that in the lower right is thin with a thickness of 4.9 nanometers. The thin membrane shows a surface roughness of 0.4 nanometers, which is close to that of the cleaned silicon substrate.Energy dispersive X-ray analysis was used to further investigate the composition of the hybrid membrane on the silicon substrate. The atomic ratios of representative elements, such as copper, phosphorous, nitrogen, and carbon are 0.33, 0.97, 4.06, and 68.56%respectively. The theoretical molar ratio of copper, to phosphorus, to nitrogen, to carbon should be one, to three, to 11, to 192, which is close to the measured element ratio in the hybrid membrane, indicating that the ratio between the lipids and the copper phthalocyanine molecules is maintained after the film formation and transfer processes.By doping the lipid membranes with other nanomaterials, such as graphene or menthol nanoparticles, nanohybrid membranes with various functions can be readily formed.

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