A Protocol for the Production of Gliadin-cyanoacrylate Nanoparticles for Hydrophilic Coating

The overall goal of this demonstration is to show a protocol for the production of protein-based nanoparticles that change hydrophobic surfaces to hydrophilic. This demonstration shows how protein-based nanoparticles for hydrophilic coating are produced, and how well they perform on the surface of the target materials. The main advantage of this technique is that the coating is done in less than a minute.

Demonstration will be done by my technician, Jason Adkins, who has been working in the USDA laboratory for the past 16 years. To begin this procedure, measure 150 milliliters of acetone with a graduated cylinder and transfer it to a 250 milliliter Erlenmeyer flask. While stirring, add 30 grams of commercial gliadin powder to the flask containing the acetone.

Seal the opening of the flask with aluminum foil and continue to the stir the solution at room temperature overnight. On the next day, filter the solution through filter paper. Then wash the retentate with approximately 50 milliliters of fresh acetone.

Following filtration, transfer the retentate and the filter paper to a square cell culture dish. Cover the dish with a piece of large filter paper to slow down the evaporation of residual acetone. After allowing the defatted gliadin to dry overnight, transfer it to an airtight container and store on the lab bench.

Now, measure 150 milliliters of deionized water with a graduated cylinder and transfer it to a 1, 000 milliliter Erlenmeyer flask. Measure 350 milliliters of absolute ethanol with a mess cylinder and add it to the flask containing deionized water. Stir the solution vigorously until air bubbles are no longer observed.

Next, add 20 grams of the defatted gliadin powder to the stirring solution. After stirring overnight, transfer the entire solution to a 1, 000 milliliter mess cylinder and allow it to sit for two days. Following this, transfer the supernatant to a round-bottomed flask with flexible tubing and remove as much ethanol from the supernatant as possible by rotary evaporation.

At this point, freeze the solution containing the gliadin aggregates by immersing the flask in a methanol dry ice mixture. Then freeze dry at 70 degrees Celsius under vacuum. Crush the freeze-dried gliadin with a mortar and pestle and grind with a coffee grinder to obtain a fine powder.

Then transfer the powder into an airtight container and store it at room temperature. For the polymerization reaction, add 3.2 grams of distilled water and 6.8 grams of absolute ethanol to a tared scintillation vial. Stir the solution vigorously until air bubbles are no longer observed.

Next, add 40 microliters of four normal hydrochloric acid to the vial while stirring. Add 20 milligrams of the purified gliadin powder and continue to stir until the powder is fully dissolved. After confirming the solution is homogeneous, slowly add 80 to 100 microliters of ethyl cyanoacrylate monomer while stirring.

Reduce the stirring speed to 500rpm and continue stirring the solution for one hour. When the reaction is complete, transfer the solution into a centrifuge tube and balance the weight of the tube. Centrifuge the sample at 10, 000 times g for 20 minutes.

Following centrifugation, transfer the produced nanoparticle suspension with a pipette to a scintillation vial and store it at room temperature. To characterize the product, prepare a 68 weight percent solution of aqueous ethanol in a 20 milliliter scintillation vial. Stir the solution until air bubbles are no longer observed.

Next, add 40 microliters of four normal hydrochloric acid and 50 microliters of the nanoparticle suspension to the solution while stirring. Now measure the size of the nanoparticles with dynamic light scattering following the manufacturer’s instructions. At this point, wash the surface of a glass plate, such as a hand mirror, with soap water.

Spray the nanoparticle suspension on part of the glass plate and immediately rinse off the surface with water. Following this, spray water on the entire surface of the glass plate. Observe the difference between the coated and uncoated surfaces.

As the ethanol content in the nanoparticle suspension decreases, the surface of each nanoparticle is highly charged, and the hydrophilicity of the particle surface is significantly increased. The SEM image of the absorbed nanoparticles shows that the nanoparticles are well-dispersed on the surface of a glass plate, and there are enough spaces between the particles for light to pass through. This spatial distribution of particles and the small particle size explain why the transparency of the glass plate is not affected by the coating.

The contact angles of glass and polystyrene before and after nanoparticle coating shows that the surface tension drops significantly after coating. The coating effect can readily be visualized by comparing the wetting effect before and after nanoparticle coating on polycarbonate. The right half, which was coated with nanoparticles, forms a thin film of water, while the left uncoated half forms water droplets, showing that water does not wet the surface.

When nanoparticle coated and uncoated auto glass windows were treated with water, a thin water layer was formed on the coated glass, while water droplets covered the uncoated glass, demonstrating that the coated glass offers better visibility. After watching this video, you should have a good understanding of how protein-based nanoparticles are prepared and how they are used to change the wetting proportion materials.