Colloidal gold synthesis results in a solution color that varies with particle size, typically ranging from deep red to dark brown/purple and light orange/yellow. The particle size can be controlled by adjusting the gold to citrate ratios, ranging from 1nm to 100nm, and the colloid remains indefinitely stable. Citrate can also be replaced by other molecules such as thiols in the synthesis process.

1. Colloidal Gold Synthesis
• Solution color varies extensively with particle size
– Usually a deep red, but also dark brown/purple to light orange/yellow
• Colloid size can be controlled by Au:Citrate ratios
– Anywhere between 1nm - 100nm +
• Indefinitely stable
• Citrate is easily substituted by other more Au-philic molecules (i.e
thiols)
OH
HO
O
OH
O
O
HO
H2O, 100OC
H2AuCl4
Cit
-
Cit
-
Cit
-
Cit
-
Turkevich, et. al. Discussions Faraday Soc. 1951, No. 11 55-75.

2. TEM Images of Colloidal Au
• Average particle size ~ 17nm