The most effective method for synthesizing gold nanoparticles with a narrow size distribution suitable for use in medical imaging is the Turkevich method, also known as the citrate reduction method. This method involves the reduction of gold salts, typically chloroauric acid HAuCl4 , using sodium citrate as both a reducing agent and a stabilizing agent.Here's a general procedure for the Turkevich method:1. Prepare a gold salt solution: Dissolve an appropriate amount of chloroauric acid HAuCl4 in deionized water to achieve the desired concentration e.g., 1 mM .2. Heat the gold salt solution: Place the gold salt solution in a round-bottom flask and heat it to boiling under reflux.3. Prepare a sodium citrate solution: Dissolve an appropriate amount of trisodium citrate dihydrate Na3C6H5O72H2O in deionized water to achieve the desired concentration e.g., 38.8 mM .4. Add the sodium citrate solution: While the gold salt solution is boiling, quickly add the sodium citrate solution to the flask. The color of the solution will change from pale yellow to deep red, indicating the formation of gold nanoparticles.5. Continue heating: Maintain the boiling temperature for an additional 10-30 minutes to ensure complete reduction of gold salts and stabilization of the nanoparticles.6. Cool and collect the nanoparticles: Allow the solution to cool to room temperature, and then collect the gold nanoparticles by centrifugation or filtration.The Turkevich method produces gold nanoparticles with a narrow size distribution, typically around 10-20 nm in diameter, which is suitable for medical imaging applications such as computed tomography CT , magnetic resonance imaging MRI , and optical imaging. The size and shape of the nanoparticles can be controlled by adjusting the concentration of the gold salt and sodium citrate, as well as the reaction temperature and time.Additionally, the surface of the gold nanoparticles can be functionalized with various ligands, such as antibodies, peptides, or small molecules, to target specific biological structures or processes, further enhancing their utility in medical imaging.