The most effective method for synthesizing gold nanoparticles AuNPs with a size range of 10-20 nm is the Turkevich method, also known as the citrate reduction method. This method involves the reduction of gold ions Au3+ to gold nanoparticles Au0 using trisodium citrate as both a reducing agent and a stabilizing agent. The Turkevich method is widely used due to its simplicity, cost-effectiveness, and ability to produce monodisperse gold nanoparticles with good control over size and shape.To optimize the Turkevich method for a high yield and stability of the resulting nanoparticles, consider the following factors:1. Concentration of gold salt HAuCl4 : The concentration of gold salt affects the size and yield of the AuNPs. A higher concentration of gold salt can lead to larger nanoparticles, but may also result in aggregation. To obtain AuNPs with a size range of 10-20 nm, a concentration of 0.25-1 mM is recommended.2. Concentration of trisodium citrate: The concentration of trisodium citrate plays a crucial role in controlling the size and stability of the AuNPs. A higher concentration of trisodium citrate leads to smaller and more stable nanoparticles. For the desired size range, a citrate-to-gold molar ratio of 3:1 to 6:1 is recommended.3. Reaction temperature: The temperature at which the reaction takes place affects the rate of reduction and the size of the nanoparticles. Higher temperatures result in faster reduction and smaller nanoparticles. To achieve the desired size range, a temperature of 80-100C is recommended.4. Reaction time: The reaction time influences the size and stability of the AuNPs. Longer reaction times can lead to larger nanoparticles and increased aggregation. For the desired size range, a reaction time of 10-30 minutes is recommended.5. pH: The pH of the reaction mixture affects the reduction rate and the stability of the AuNPs. A pH range of 4-6 is recommended for optimal synthesis.6. Aging: Allowing the synthesized AuNPs to age for a period of time e.g., 24 hours can improve their stability.7. Purification: To remove excess reactants and byproducts, the AuNPs can be purified using centrifugation or dialysis.By optimizing these factors, the Turkevich method can be used to synthesize gold nanoparticles with a size range of 10-20 nm, with a high yield and stability.