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

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.