I am synthesizing AuNPs in the size range of 5 to 8 nm by using DDAB didodecydimethyllammonium bromine and DDT didodecylamine and reducing agent is hydrazine. This seed mediated method of synthesis of AuNPs followed by many good references. But I am facing problem in seed solution synthesis, seed solution reduction can happen by using tetrabutylammonium bromide at 25 degreeC, while the color of seed solution is not changing from yellow brown. Second, problem is when i add hyrdazine dropwise in growth solution for synthesis of AuNPs with vigorous stirring, then after 10 minutes of addition i get aggregation (black color precipitates) I have tried different ways but problem is still there. So Please related field Researchers can give me some suggestions? Thanks