One-pot synthesis of gold nanorods by ultrasonic irradiation: the effect of pH on the shape of the gold nanorods and nanoparticles.

A novel one-pot synthesis method to prepare gold nanorods was developed by using sonochemical reduction of gold ions in aqueous solution. The size of the sonochemically formed gold nanorods was less than 50 nm, and their average aspect ratio decreased with increasing pH of the solution. The aspect ratio measured was 3.0 at pH 3.5, 2.2 at pH 5.0, and 2.1 at pH 6.5. At pH 7.7, irregular shaped gold nanoparticles were formed. At pH 9.8, most of the particles formed had a spherical shape with a smaller particle size than those formed in the lower pH solutions. Based on the obtained results, it was clear that the size and shape of the sonochemically formed gold nanoparticles are dramatically dependent on the pH value of the solution.