Synthesis of Colloidal Gold
This lab was adapted for use with the SALS Device by Lisa Goetter.
The experiment was obtained from the MRSEC website Video Lab Manuel.
Copyright © 2006University of Wisconsin – Madison
The formation of gold nanoparticles can be observed by a change in color since small nanoparticles of gold are red. A layer of absorbed citrate anions on the surface of the nanoparticles keep the nanoparticles separated. Switching to a smaller anion through using NaCl allows the particles to approach more closely and another color change is observed.
To synthesize gold nanoparticles
To understand the change in properties of gold nanoparticles
To run an oxidation – reduction reaction
To use the SALS Device
The formation of colloidal gold occurs by using citrate to reduce gold (III) to gold solid. The reduction half reaction of gold is shown below:
Au3+ (aq) + 3e- → Au (s)
1.0mM hydrogen tetrachloroaurate – HAuCl4 (s)
1% trisodium citrate – Na3C6H5O7 ∙ 2H2O (s)
1 M NaCl – NaCl (s)
Note: HAuCl4 (s) can be purchased online through Sigma Aldrich – ten grams for $112.50. www.sigmaaldrich.com. You may also want to contact the local university as they will usually have access to hydrogen tetrachloroaurate.
Trisodium citrate, commonly known as sodium citrate, is a common food additive that can be found at specialty food stores.
1 30mL beaker
Flea stir bar
2 10mL beakers
Stirring hot plate with white porcelain top
Ring stand with 3-prong clamp (optional)
Note: The white porcelain top on the hot plate is needed to obtain a good reading with the SALS Device.
Wear eye protection
Use care with the stir/hot plate
Preparation of Stock Solutions
For 1.0mM hydrogen tetrachloroaurate: Dissolve 0.1g HAuCl4 in 500mL distilled water. This stock solution of gold (III) ions can be prepared in advance if stored in a brown bottle.
For 1% trisodium citrate: Dissolve 0.5 g Na3C6H5O7.2H2O (sodium citrate) in 50 mL distilled water.
For 1 M NaCl: Dissolve 0.5 g of NaCl in 10 mL distilled water
(This procedure prepares enough stock solution for 25 batches.)
A. D. McFarland, C. L. Haynes, C. A. Mirkin, R. P. Van Duyne and H. A. Godwin, "Color My Nanoworld," J. Chem. Educ. (2004) 81, 544A.
Lisensky, George. “Synthesis of Colloidal Gold” Video Lab Manual. MRSEC Interdisciplinary Education Group. 2005. Beloit College. 6 July 2006. <http://www.mrsec.wisc.edu/Edetc/nanolab/gold/index.html>.