Tris base assisted synthesis of monodispersed citrate-capped gold nanospheres with tunable size

Abstract

We demonstrate a simple and effective method to obtain highly pure and monodispersed spherical gold nanoparticles (AuNPs) with a narrow size distribution (RSD ∼ 4–7%) in aqueous medium. The synthetic strategy involves the addition of HAuCl₄ in preheated sodium citrate (SC) solution followed by addition of tris base (TB) which simultaneously acts as stabilizer, mild reducing agent and pH-mediator. A significant improvement in the uniformity and size tenability of the Au nanospheres has been observed by using subtle amounts of TB in contrast to the conventional way of using only SC. It is their synergistic effect that controls the amount of nuclei by heating SC, and then controlling the rate of nucleation and growth by introducing TB, which successfully produced particles with uniform morphology. Notably, HAuCl₄ solution was added in multiple steps to significantly improve the quality of the NPs in comparison to the addition of whole HAuCl₄ solution at one time. In this way, we have successfully developed spherical NPs with sizes ranging from 20 to 115 nm, which efficiently improve the classical Turkevich/Frens method with respect to the reproducibility and uniformity of the NP's size and shape. A representative set of NPs was controlled to spontaneously self-assemble into a monolayer assembly at a hexane/water interface. This will allow them to be used as a promising and outstanding candidate for application in the field of spectroscopy, catalysis, optoelectronic nanodevices and biosensors.