Monodisperse sub-10Â nm gold nanoparticles by reversing the order of addition in Turkevich method - The role of chloroauric acid

► Monodisperse 5-10 nm size nanoparticles were prepared using sodium citrate as the reducing/stabilizing agent. ► Reversing the order of addition used in the Turkevich method results in monodisperse nanoparticles. ► Chloroauric acid reactivity plays a key role by controlling the rate of oxidation of citrate into acetone dicarboxylic acid. ► The system exhibits a 'memory' of the order of addition, even for conditions resulting in slow reduction.