Preparation of 12nm Gold Particle Sols

Prepare 5 ml of a 1 percent HAuCU solution in deionized water. 

Add 4 ml of the chloroauric acid solution plus 4 ml of 0.1 M K2CO3 to 100 ml deionized water. Mix well and cool the solution on ice. 

With rapid mixing of the chloroauric acid/carbonate solution, quickly add 1ml of a 7 percent sodium ascorbate solution prepared in water. Maintain the solution cooling in an ice bath. Higher temperatures will create larger particle sizes. The color of the solution at this point will turn to a purple-red. 

Adjust the volume of the reaction to 400 ml with deionized water. 

Bring the mixture to a boil and reflux until the color of the suspension turns from purple-red to red. 

---