University of Illinois, Urbana-Champaign
North Carolina A&T State University, Greensboro
University of California - Irvine
Stanford University, Palo Alto
University of Notre Dame
Northwestern University
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 jmuskin@uiuc.edu.
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
Click on the image above to open a full sized version.
Experimental Procedure
Make gold and silver nanoparticles.
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.
Add 5 drops of 1% sodium citrate to both the test tubes.
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)
Remove test tubes and set in a test tube rack to cool.
Test nanoparticle size.
Check for Tyndall effect using a laser pointer, check gold, silver, and a test tube of clean water.
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.
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
Change the spacing between the gold nanoparticles using NaCl.
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.
Visualize collected nanoparticles.
Cut open blue gold filter across seam using a razor blade.
Cut open silver filter across seam using a razor blade
Downloadable Materials:
Activity Guide
Instructors guide containing all relevant information to conduct the lab.
Jpeg images of various steps of the activity for teachers to use to create their own documents. Multiple pictures have been "zipped" into a single archive. You will need softare to "unzip" the archive. If you need assistance, please contact the web master.
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.
