Synthesis of Cd-free InP/ZnS Quantum Dots Suitable for Biomedical Applications

The overall goal of this procedure is to Synthesize Highly Fluorescent Indium Phosphide Zinc Sulfide Quantum Dots that are suitable for Biomedical Applications. This method can help clarify key questions about the Synthesis of Quantum Dot Nanoparticles by demonstrating specific steps that are crucial to achieve high quality Quantum Dots. The main advantage of this technique is the production of high quality, water soluble Quantum Dots.

Viable for biological systems that can be synthesized in less than one day. To begin synthesis, fit a 100 milliliter round-bottom, three-neck flask with a 12-inch condenser. 0.398 grams of Indium Chloride, 30 milliliters Oleylamine, or OLA, and 0.245 grams of Zinc Chloride.

Stir while evacuating at room temperature using a vacuum for one hour. The solution should appear colorless with a white precipitate. Use a heating mantle with a Thermocouple and PID Temperature Controller to increase the temperature of the solution to 120 degrees celsius.

Use of a heating mantle and PID increases the uniformity and reproducibility of the reaction product. Evacuate the solution under vacuum for 20 minutes to remove low boiling point impurities that may affect core growth. Under inert gas, reflux the solution and increase the temperature to 223 degrees celsius for 15 minutes.

The Indium Chloride and Zinc Chloride completely dissolve resulting in a pale yellow solution. Allow the temperature to stabilize for 10 minutes. Next, purge a disposable three milliliter plastic syringe and 4-inch 22 gauge needle with Nitrogen gas.

The injection of TDMAP is a critical step in this procedure as the injection can greatly affect the dispersity of the resulting Indium Phosphide Quantum Dots. Using the syringe, quickly deliver 0.5 milliliters of TDMAP to the Indium Chloride solution. The solution temperature decreases slightly and returns to 220 degrees celsius while the solution changes from transparent pale yellow to opaque black.

After nine and a half minutes, remove the reaction flask from the heating mantle until the temperature decreases below 200 degrees celsius. To protect the integrity of the Indium Phosphide cores proceed directly to the Zinc Sulfide coating. Place the reaction flask containing the Indium Phosphide Quantum Dots on a heating mantle and stabilize the temperature at 200 degrees celsius.

Slowly add 3.58 grams of DDT to the solution over the course of 15 seconds. After allowing the solution to react for one hour, remove the reaction flask from the heating mantle and allow the solution to cool for approximately 60 degrees celsius. Once the Indium Phosphide Zinc Sulfide solution reaches approximately 60 degrees celsius, add 10 milliliters of Hexanes.

Then, transfer the entire solution of roughly 45 milliliters to a 50 milliliter polypropylene centrifuge tube. Centrifuge the sample to remove unreacted solid precursors. Carefully remove the Supernatant and add 200 milliliters of Acetone.

Equally divide the resulting solution into four 15 milliliters centrifuge tubes. Then, centrifuge the solution to precipitate the Indium Phosphide Zinc Sulfide Quantum Dots. Decant the supernatant and dry the Quantum Dot pellet thoroughly with Nitrogen gas to remove Acetone.

Then, we suspend the Quantum Dots in 20 milliliters of OLA using Sonication. Then, transfer the resuspended Quantum Dots to a 50 milliliter round-bottom three-neck flask containing 0.474 grams of Zinc Stearate and stir. Evacuate the solution under vacuum for 20 minutes at room temperature.

Under Nitrogen gas, increase the temperature to 180 degrees celsius and allow the reaction to proceed for three hours. Upon completion of the reaction, remove the flask from heating mantle and allow the solution to cool to approximately 60 degrees celsius. Once the Indium Phosphide Zinc Sulfide solution reaches approximately 60 degrees celsius, add 20 milliliters of Hexanes.

Then, transfer the sample to a 50 milliliter polypropylene centrifuge tube before centrifuging to remove unreacted Zinc Stearate. Following centrifugation, add 200 milliliters of Acetone to the Supernatant and centrifuge using the same procedure as before. After thoroughly drying the pellet with Nitrogen gas, to remove the Acetone, dissolve the Indium Phosphide Zinc Sulfide Quantum Dot pellet in 30 milliliters of Hexanes.

Vortex and sonicate the solution briefly to ensure complete dispersion. Removing the excess ligands is a critical step in this procedure. Failure to do so will negatively impact the efficiency of transferring the Quantum Dots into aqueous solutions using PMAL-d Repeat these purification steps two more times to ensure thorough removal of excess organic ligands.

Interactions between the Amphiphilic Polymer and the Quantum Dot can be compromised in the presence of excess ligands. Following purification, determine the size and concentration of the synthesized Indium Phosphide Zinc Sulfide Quantum Dots using UV-Visible Spectroscopy. Dilute a portion of the synthesized Indium Phosphide Zinc Sulfide Quantum Dots with Hexanes to obtain one milliliter of one micromolar Quantum Dots.

In a centrifuge tube, transfer 0.25 milliliters of Indium Phosphide Zinc Sulfide Quantum Dots into each tube. Add one milliliter of Acetone or menthol to the centrifuge tube, and centrifuge. Carefully remove the supernatant and dissolve each precipitate in one milliliter of Tetrahydrofuran or THF.

Next, transfer the Indium Phosphide Zinc Sulfide Quantum Dots dissolved in THF into a 100 milliliter round-bottom flask and dilute with 16 milliliters of THF. To reduce the number of aggregates in solution, sonicate the Quantum Dots for five to ten minutes. Then, dissolve 30 milligrams of PMAL-d and 10 milliliters of molecular grade water.

Water about sonication or gentle stirring until the solution is translucent is efficent to completely dissolve the polymer. The use of Vortex or a vigorous stirring can produce many bubbles which hinders interaction of the polymer with the Quantum Dot. Next, add the 10 milliliter polymer solution to the 100 milliliter round-bottom flask containing Indium Phosphide Zinc Sulfide Quantum Dots and THF.

Evaporate the THF from the Quantum Dot polymer solution using a Rotary Evaporator with the flask in an ice bath to facilitate the interaction between the polymer and Quantum Dot. Once the solution is evaporated to 10 milliliters, remove the flask from the Rotary Evaporator and add 30 milliliters of molecular grade water. Return the flask to the Rotary Evaporator and continue to evaporate to two milliliters.

This final evaporation step may take many hours. Ensure the ice bath is maintained. Remove the water soluble Indium Phosphide Zinc Sulfide Quantum Dots from the round-bottom flask with a pipette.

Filter the Quantum Dot solution into a five milliliter centrifuge tube using a three milliliter plastic syringe attached to a 0.1 Micron Nylon Syringe Filter. Place the Quantum Dots into a 20 thousandth molecular weight cutoff membrane dialysis unit and dialyze against 05 Molar Borate Buffer, PH 8.5, to remove excess polymer. Using a vacuum concentrator, concentrate the Quantum Dots and Borate Buffer to one milliliter.

For storage, perch the solution with Nitrogen gas before sealing with Parafilm. The water soluble Indium Phosphide Zinc Sulfide Quantum Dots are stable for at least four months at four degrees celsius in the dark. Shown here is the absorbance and corrected Florescence Admission Spectra of Indium Phosphide Zinc Sulfide Quantum Dots and Hexanes excited at 533 nanometers showing a maximum absorbance at 600 nanometers and a full width at half maximum of 73 nanometers.

Here a TEM, or Transmission Electron Microscopy Image, of the Indium Phosphide Zinc Sulfide Quantum Dots dissolved in water is shown. A particle size distribution historgram of the TEM results in an average diameter of 2.74 plus or minus 0.72 nanometers. Single Florescent Puncta Analysis details the presence of distinct on and off states through a blinking profile of Indium Phosphide Zinc Sulfide Quantum Dots in water.

This histogram exhibits the bimodal distribution of Pixel Intensity from one Quantum Dot blinking profile. Here a graph depicts the viability of N2a cells after incubation with Indium Phosphide Zinc Sulfide Quantum Dots for 24 or 48 hours. With one nanomolar to 25 nanomolar Quantum Dots.

Negligible toxicity is observed below five nanomolar. Once mastered, this techniques can be completed in 12 hours if it is performed properly. After watching this video, you should have a good understanding of how to synthesize Highly Fluorescent Quantum Dots for use in Biomedical applications.

Note that Allylamine is a hazardous, corrosive organic compound. Precautions such as wearing googles, gloves and a lab coat should always be taken when performing this procedure.