21479
Colloidal gold nanoparticles were prepared using two methods : either with citrate molecules ( Turkevich method ) or with ascorbic acid as the surfactant .
 citrate, ascorbic acid
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 citrate, ascorbic acid