Optimizing a Novel Method for Synthesizing Gold Nanoparticles

Background: The properties of Gold Nanoparticles (GNPs) make them useful for cancer therapy, diagnostics and imaging. For the application of GNPs in therapy and drug delivery there is a great necessity to synthesize known particle size of GNPs with simple methods. This study aimed to optimize a novel simple method for synthesizing GNPs. Methods: GNPs were synthesized by using different citrate concentrations (40, 100 and 150 mM) through reduction of hydrogen tetrachloroaurate (HAuCl 4 ) of varying concentrations. The synthesized GNPs were characterized with transmission electron microscope, UV-Vis spectrophotometer, and size distributions with dynamic light scattering. Results: At 40 mM citrate concentration, different particle sizes (18-28 nm), non-round and not homogenous GNPs were formed; at 100 mM citrate concentration, more round GNPs were formed and the particle size reduced to nearly 12 nm with very narrow particle size distribution; at 150 mM citrate concentration, the GNPs size increased up to 18 nm and the homogeneity of the particle size distribution reduced as indicted from both Transmission Electron Microscopy (TEM) image and distribution profile. When HAuCl 4 concentration increased from 1 to 4 mM, the particle size of GNPs increased from 12 nm to nearly 20 nm, respectively. Conclusions: At 40 mM citrate concentration, the coverage of citrate is incomplete and the aggregation process leads to the formation of inhomogenous GNPs; at 100 mM citrate concentrations, the citrate behaves as a pH mediator explains the reduction of the particle size. The increase of HAuCl 4 concentration causes retardation of the nucleation step forming lower number of nuclei in the solution and thus increases the final particle size and polydispersity.