User:James C. Schwabacher/Notebook/Protein-Templated Quantum Dots/2015/02/27

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Project Summary

  • Adapted from Goswami et. al
  • We set out to synthesize mercury-sulfide quantum dots templated by Bovine serum albumin. Multiple attempts proved unsuccessful. However, in the process we discovered a reproducible synthesis that yields, what appears to be, a protein-based film suspended in aqueous solution. This page summarizes all of my experiments conducted during the 2014-2015 academic year, as well as my optimized synthesis procedure for producing these HgS-BSA films (aka the "Quick Synthesis").
  • A few times throughout my notes I refer to the films formed as hydrogels or sol-gels. The sol-gels classification is incorrect, and, from what I can tell working with these materials, hydrogel may be the most appropriate category.
  • You will find UV-Vis and Fluorescence data for the first few syntheses (JCS 1-3) in an excel file on DropBox. This file also contains FTIR data from JCS 16. The sample was stuck to the membrane that was used to filter it, so a spectra of the membrane is also included.
  • There is a folder containing the DSC data for films JCS 4 and JCS 5 on DropBox.
  • You will also find a folder containing powder XRD data for the films produced from JCS 4 and JCS 5. However, something went wrong with the DSC protocol during the runs so these results should be scrutinized.
  • While I previously reported preparing a DSC sample with one of the later reactions (I recorded the pan mass, etc.), this sample was never run. The instrument was not working at the time and the sample sat for too long by the time the DSC was up and running.
  • A collection of images taken throughout the year have been labeled and uploaded to DropBox as well.
  • Note: Un-rotovapped samples that were left sitting in the scintillation vials in the cold room formed a layer of precipitate on the bottom of the glass. The best way to describe these structures is 'shiny aluminum foil.'

Original Protocol

  1. Prepare at least 5 mL of 15 mg/mL BSA in deionized water.
  2. Prepare at least 5 mL of 5 mM Mercury (II) nitrate in deionized water.
  3. Pour 5 mL of the BSA solution into a 25 mL round bottom flask; stir this solution in the hood.
  4. Vortex the mercury solution (to help the compound dissolve) and add 5 mL of the solution to the round bottom (while stirring).
  5. Add a few drops of 1 M NaOH to the stirring mixture to achieve ~pH 9. (I most commonly ended up with a pH of 10).
  6. Allow 8-12 hours to pass.
  7. Prepare 5 mL of 20 mM sodium sulfide.
  8. Add 4 mL of 20 mM sodium sulfide to the round bottom (while stirring).
  9. Allow 15 minutes to pass
  10. Transfer to a larger round bottom flask and rotovap the solution with a water bath set to ~40°C.
  11. Once completely dry (a thin film will develop along the sides of the flask), remove from the rotovap.
  12. Slowly add a few mL of DI water while gently swirling the round bottom flask. First, a hydrogel network should form along the sides of the glass as the film rehydrates.
  13. Slowly add more DI water until the hydrogel detaches from the glass and collapses into sol-gel structures suspended in solution.

"Quick" Protocol (15 min Synthesis)

  1. Prepare at least 5 mL of 15 mg/mL BSA in deionized water.
  2. Prepare at least 5 mL of 5 mM Mercury (II) nitrate in deionized water.
  3. Prepare 5 mL of 20 mM sodium sulfide.
  4. Pour 5 mL of the BSA solution into a 25 mL round bottom flask; stir this solution in the hood.
  5. Vortex the mercury solution (to help the compound dissolve) and add 5 mL of the solution to the round bottom (while stirring).
  6. Add a few drops of 1 M NaOH to the stirring mixture to achieve ~pH 9. (I most commonly ended up with a pH of 10).
  7. Immediately add 4 mL of 20 mM sodium sulfide to the round bottom (while stirring).
  8. Allow 15 minutes to pass
  9. Transfer to a larger round bottom flask and rotovap the solution with a water bath set to ~40°C.
  10. Once completely dry (a thin film will develop along the sides of the flask), remove from the rotovap.
  11. Slowly add a few mL of DI water while gently swirling the round bottom flask. First, a hydrogel network should form along the sides of the glass as the film rehydrates.
  12. Slowly add more DI water until the hydrogel detaches from the glass and collapses into sol-gel structures suspended in solution.

Note: These solutions have a tendency to bump on the rotovap. Watch carefully and be ready to break vacuum temporarily in the beginning!

Filtration Protocol

I conducted vacuum filtration once using a membrane filter (Supor-450, 47mm, 0.45μm). This worked to separate the gels from the solution, however do not leave the product on the membrane to dry--it will get stuck the membrane.

Summary of Syntheses Attempted

Date Batch Reaction Temp (C) Reaction Time (hrs) Notes Gel Formation?
9/9/2014 JCS 1 23 11.58 no heating Not Attempted
9/16/2014 JCS 2 41 mantle setting 11 Not Attempted
9/23/2014 JCS 3 37 13.5 mantle setting 10 Not Attempted
9/30/2014 JCS 4 23 11.5 no heating Yes (first discovery)
9/30/2014 JCS 5 50 11.5 mantle setting 14.5 Yes
10/7/2014 JCS 6 23 11 no heating Not Attempted
11/4/2014 JCS 7 23 no heating, BSA Control No (Structures did form but were noticeably different)
11/11/2014 JCS 8 23 7.5 Hg into BSA Not Attempted
11/11/2014 JCS 9 23 7.5 BSA into Hg Not Attempted
11/11/2014 JCS 10 Cold Room 7.5 cold room synthesis- no change Not Attempted
11/18/2014 JCS 11 23 48 attempting gel formation again Yes
11/18/2014 JCS 12 23 48 attempting gel formation again Yes
1/22/2015 JCS 13 23 24 No Mercury No
1/29/2015 JCS 14 23 Over Weekend No Sodium Sulfide No (similar to BSA-only)
2/4/2015 JCS 15 23 24 No BSA No (black precipitate)
2/5/2015 JCS 16 23 15 minutes original protocol with changed timeline Yes
2/20/2015 JCS 17 23 15 minutes Decreased BSA conc (x10) No

Determining Sol-Gel formation factors

Sample BSA Mercury NaOH Sulfide Overnight Temp Formed?
JCS13 X X X X Room No
JCS14 X X X X (over weekend) Room No
JCS15 X X X X Room No
JCS16 X X X X Room Yes
JCS17 X (decreased factor of 10) X X X Room No