Gold and Silver Nanoparticles

In this lab, students will make and filter three different gold and silver colloidal mixtures. Gold and silver solutions will be reduced and stabilized with sodium citrate in a boiling water bath. The colloidal dispersions formed will be poured into Petri dishes, drawn into a Luer-Lok™ syringe, and filtered through 20 nm pore size ceramic filters. The colloidal gold should be deep red in color and pass through the filter. Gold colloid particles are about 13 nm in size. The silver colloid should be yellow in color and get caught in the filter. Silver colloidal particles are 20-50 nm in size. If the silver filter is cut open along the seam with a single edged razor blade, the silver metal can be seen on the inside of the filter. Interestingly, the color will be the color of bulk silver, not the yellow color of the colloid. The red gold colloid in the filtrate can be coagulated into larger particles using sodium chloride. This will change the color of the gold colloid from red to blue. The blue gold colloid can then be refiltered and the students will find that it will be caught on the filter. Cutting open the filter will reveal the gold color of the metal. From their observations, students can draw conclusions about the sizes of red and blue gold and yellow silver colloids.

If you have any questions about this lab, please contact Joe Muskin at (217) 265-6481 or by email at .

Purpose:

Nanoparticles have many applications and are important in an area of research known as nanotechnology. Use of gold nanoparticles shows promise as a cancer treatment, whereas silver nanoparticles are useful for killing microbes. In this activity, students will make gold and silver nanoparticles and filter them with ceramic filters having 20-nm pores. Students will then draw about the sizes of the nanoparticles.

Materials:

  • .5 mM Au3+ solution
  • .5 mM Ag+ solution
  • 1% Sodium citrate solution
  • Disposable 3 mL pipettes
  • Hot plates
  • 250 mL beakers
  • Anotop® 10 filters
  • 3 mL syringes
  • Razorblade
  • Petri dishes
  • Sodium Chloride
  • Test tube holders
  • Test tube rack
  • Millipore water
  • Laser pointers
Various laboratory equipment for use within the lab.

Click on the image above to open a full sized version.

Experimental Procedure

  1. Make gold and silver nanoparticles.
    1. Add 2 mL of 1mM AgNO3 to a small test tube, add 2 mL of 0.5mM HAuCl4 to another test tube. Place the test tubes in a 250-mL beaker of boiling water for 10 minutes.

    2. Add 5 drops of 1% sodium citrate to both the test tubes.

    3. Continue to heat until the gold changes a wine red color and the yellow turns a yellowish. (should take ~5 minutes for gold, ~15 minutes for silver)

    4. Remove test tubes and set in a test tube rack to cool.

  2. Test nanoparticle size.
    1. Check for Tyndall effect using a laser pointer, check gold, silver, and a test tube of clean water.

    2. Draw about 0.5 mL of gold nanoparticles into a syringe, follow with about 1 mL of air. Attach filter to end of syringe. Push nanoparticle solution through the filter, try to determine if the nanoparticles pass through.

    3. Draw about 0.5 mL of silver nanoparticles into a syringe, follow with about 1 mL of air. Attach filter to end of syringe. Push nanoparticle solution through the filter, try to determine if the nanoparticles pass through

  3. Change the spacing between the gold nanoparticles using NaCl.
    1. Add a few grains of NaCl to silver nanoparticles, mix gently. Draw about 0.5 mL of gold nanoparticles into a syringe, follow with about 1 mL of air. Attach filter to end of syringe. Push nanoparticle solution through the filter, try to determine if the nanoparticles pass through.

  4. Visualize collected nanoparticles.
    1. Cut open blue gold filter across seam using a razor blade.

    2. Cut open silver filter across seam using a razor blade

Downloadable Materials:

  • Presentation
    Presentation for teacher to introduce the activity to students.

  • Procedure
    Procedure with pictures of each step.

Safety:

Goggles, gloves and aprons should be worn as in all chemistry laboratory activities. The hot water baths should be handled with care to avoid burns. Any liquids spilled on skin can be washed off with water. The most dangerous part of this lab is opening the ceramic filters to reveal the metals on the inside surfaces. This requires cutting open the filter while it is still attached to the syringe. Cutting along the seam of the filter with a single- edged razor blade will reveal the inside of the filter. Because of the danger of cutting oneself with the razor blade, this part of the procedure should be performed by the instructor.

Acknowledgements:

Thanks to Scott Robinson and Chas Conway of the Microscopy Suite, part of the Imaging Technology Group at the Beckman Institute of Advanced Science and Technology, University of Illinois Urbana-Champaign for SEM images and experiment photographs.

Thanks to Martha Atwater and Carrie Kouadio for helping organize, design and edit the teaching resources.

Developers

David Bergandine, Tom Gelsthorpe, Terry Koker, Joe Muskin, and Matt Ragusa