Manipulating the Anisotropic Structure of Gold Nanostars using Good's Buffers

This paper describes a set of design parameters for manipulating the branch length, branch direction, and overall size of gold nanostars (AuNS) synthesized by a seedless process. We controlled the structure of AuNS by varying four different synthetic factors: mechanical agitation, type of Good's buffer, concentration ratio of precursors, and pH of growth solution. We found that stirring the precursors increased the yield of branched particles. Additionally, the AuNS morphology could be controlled by changing the buffer type and concentration ratio of precursors, which tuned the localized plasmon resonances from the visible to the near-infrared. We determined that performing the synthesis at a pH less than the pK_a of the buffer was critical for the stability of the AuNS; when the pH was greater than the pK_a, the nanoparticles aggregated in solution. We expanded the library of Good's buffers able to form AuNS and optimized the mechanical and chemical synthesis conditions, which improved the structural homogeneity and overall colloidal stability of the particles.