Size-Controlled Green Synthesis of Highly Stable and Uniform Small to Ultrasmall Gold Nanoparticles by Controlling Reaction Steps and pH

Synthesis of gold nanoparticles (AuNPs) with controllable particle size and stable dispersion through green chemistry without using toxic regents is crucial for biomedical applications. In this study, spherical AuNPs with controllable particle size in the range of 8 to 18 run were synthesized by the reduction of HAuCl4 using only fruit juices/extract without adding any other chemicals. By controlling the chemical reaction steps and adjusting the pH of the solution at a later stage of the reaction, the sizes of the spherical AuNPs were fine tuned to 4.5 +/- 2.0 rum 5.9 +/- 2.5 rim, and 6.0 +/- 1.5 nm with fruit juices/extract of A. deliciosa, P. persica, and M.. domestica, respectively. For the first time, spherical ultrasmall AuNPs of 2.6 +/- 1.1 nm with uniform distribution were successfully achieved using M. Acuminate extract;at pH 10 and 11. The ultrasmall and small AuNPs were imaged again by transmission electron microscopy (TEM) after 4 months stored at the room temperature and 72 h incubation in 1 mM NaCl, which is typically found in biological media. No aggregation was observed in the above AuNP solutions after four months and incubation for 72 h in NaCl. These results indicate that highly stable AuNPs synthesized through green chemistry can be used in cells or embryos and hold great promise in biological applications.