Fabrication of Spherical and Worm-shaped Micellar Nanocrystals by Combining Electrospray, Self-assembly, and Solvent-based Structure Control

The overall goal of this procedure is to fabricate micellar nanocrystals by combining top-down electrospray, bottom-up self-assembly, and an inexpensive solvent-based method of structure control. This method offers a good way to produce an emerging class of nanobiomaterials known as micellar nanocrystals, which can be useful for biomedical detection, imaging, and therapy. The main advantages of this technique include, firstly, it’s a continuous process.

Second, it produces high quality products. And thirdly, it has an inexpensive way of controlling structure. Potentially, this technique could be adapted to produce other types of nanomaterials as well.

To begin the procedure, dissolve 10 milligrams of hydrophobic quantum dots in 20 milliliters of either chloroform or tetrahydrofuran, depending on the desired micelle shape. Vortex the solution for 20 seconds. Next, dissolve 100 milligrams of polystyrene block polyethylene glycol in 10 milliliters of either chloroform or THF, depending on the desired shape.

If the solution is in chloroform, vortex it for 20 seconds. If the solution is in THF instead, sonicate it in a bath sonicator for two minutes. Combine one milliliter of the quantum dot solution with one milliliter of the PS peg solution.

Vortex the mixture for one minute, and then draw the solution into a five milliliter PTFE syringe labeled Syringe A.Next, combine 400 milligrams of polyvinyl alcohol with 10 milliliters of deionized water. Stir the mixture at 60 to 80 degrees Celsius for four to five hours. Then, allow the PVA solution to cool to room temperature.

Draw the cooled PVA solution into a five milliliter PTFE syringe labeled Syringe B.To begin setting up the coaxial electrospray system, insert the 27-gauge stainless steel inner capillary into the 20-gauge stainless steel outer capillary assembly. Gently screw the inner capillary into position until it just meets resistance, being careful not to overtighten. Load Syringe A into a syringe pump.

Connect the syringe to the inner capillary of the coaxial nozzle with 37 centimeters of PTFE tubing. Load Syringe B into another syringe pump, and connect the syringe to the outer capillary with 17 centimeters of PTFE tubing. Position the coaxial nozzle tip about 0.8 centimeters above a steel wire ring, with a diameter of 1.5 centimeters fixed to a metal rod.

Place a 25 millimeter by 125 millimeter circular glass collection dish on a stand approximately 10 centimeters below the nozzle tip. Ensure that the direct current high voltage power supply is turned off. Then, ground the steel ring by connecting it to the negative terminal of the power supply.

Finally, connect the positive terminal of the power supply to the inner needle of the coaxial nozzle. Set syringe pump A to 0.6 milliliters per hour, and syringe pump B to 1.5 milliliters per hour. Start both syringe pumps and wait for the flow rates to stabilize, as indicated by drops forming at the nozzle at a steady rate.

Verify that there are no air bubbles in the tubing and that there are no leaks. Then turn on the system power supply. Adjust the applied voltage, staying between five and nine kilovolts, until a properly formed tailor cone is observed at the coaxial nozzle tip.

Then, place 10 milliliters of deionized water into a new collection dish. Replace the collection dish in the assembly with a new dish. Allow the electrospray process to run for 40 minutes when producing spherical micelles, or 90 minutes when producing wormlike micelles.

Then remove the collection dish. Stop the syringe pumps and turn off the power supply. Let the product dish sit uncovered in a fume hood overnight to allow the organic solvent to evaporate.

Then, transfer the product to a 15 milliliter centrifuge tube for characterization or use. Store the product at four degrees Celsius for up to one month. Transmission electron microscopy of micelles produced in chloroform revealed spherical particles with a low encapsulation number of nanocrystals.

The particle size was approximately 35 nanometers. Proper tailor cone formation was essential for micelle self-assembly. An improperly formed tailor cone resulted in overall unsuccessful production.

When THF was used as the organic solvent, wormlike micelles formed from the fusion of self-assembled spherical micelles. After 90 minutes, nearly all observed micellar nanocrystals were in wormlike shapes. The use of THF also resulted in greater nanocrystal encapsulation than was observed in chloroform.

After watching this video, you should have a good understanding of how to make micellar nanocrystals of different shapes using our fabrication method, which is scalable, inexpensive, and gives good quality of products.