Synthesize two different sets of gold nanoparticles. In one set, Au3+ is reduced by a protein (bovine serum albumin, BSA) and the synthesized nanoparticle is also surrounded and stabilized by BSA. In the second set, Au3+ is reduced by citrate, and the AuNP is stabilized by citrate in solution. The BSA-AuNPs are purple in color and the citrate-AuNPs are more of a burgundy (reddish) color.
From Dr. Hartings
Part 1: BSA-AuNP Synthesis
- Add 1.00 ml of 2.54 mM gold solution (HAuCL4) to a 10 ml volumetric flask.
- Add 1.81 BSA (90x more gold than BSA) to the volumetric flask.
- Add 7.19 ml deionized water to the volumetric flask.
- Transfer the solution to a test tube and cap with aluminum foil.
- Heat in the oven at 80°C for three hours.
- Transfer the solution to a plastic falcon tube.
Part 2: Citrate-AuNP Synthesis
- Take 50 ml of 0.254 mM gold solution (HAuCL4) from the stock solution.
- Heat the solution to boiling while stirring and covered with a watch glass.
- Add 1.5 ml of 1.01% (w/v) sodium citrate.
- Boil the solution for another 40 minutes.
- Cool to room temperature and measure the final volume.
- Determine the final concentration of gold and citrate.
- Spectrum from UV-VIS of 50x Diluted Citrate-AuNP Solution
Matt Hartings In the future, your spectra are going to be much easier to read if they only have lines (and no symbols).
Calculations from Part 2
- The absorbance of the citrate-AuNP solution was determined by first determining the absorbance of a blank sample. The absorbance of the citrate-AuNP solution was correct by subtracting the absorbance of the blank sample.
- In order to determine the molar absorptivity, ε, this reference was used. The peak appeared at 520 nm on the UV-VIS spectrum with a corresponding absorbance of 0.02. Using the ratio, Aspr/A450, it was determined that the nanoparticle diameter was 12 nm. This diameter is associated with a molar absorptivity of 1.09x108 M-1cm-1 as stated in the reference.
- Using Beer's Law, A = εbc, the concentration of the diluted solution was calculated to be 1.83x10-10 M.
- The concentration of gold in the original solution was calculated to be 1.97x10-9 M.
- The final volume of Citrate-AuNP solution was 31.0 ml.
Matt Hartings based on this final volume (and initial concentration) what is your concentration of gold?
- The progression of color change in Part 2 was light purple → dark purple → magenta → burgundy → deep red.
- The final color of the BSA-AuNP solution was dark purple.