Making sense of the mayhem behind shape control in the synthesis of gold nanoparticles.

The formation of anisotropic Au nanoparticles predominantly follows one of two growth pathways: (1) kinetic control or (2) selective surface passivation. This Perspective describes the mechanisms that control Au nanoparticle shape via these pathways in the context of three basic chemical parameters: metal complex reduction potential, metal ion availability, and adsorbate binding strength. These chemical parameters influence the crystallinity and surface facets of the Au nanoparticles, thus dictating particle shape. Understanding nanoparticle growth mechanisms in terms of simple chemical principles enables mechanistic insights to be more easily applied to other syntheses and gives them greater predictive power in the development of new preparations of metal nanoparticles with well-defined shapes. Background information regarding the growth of Au nanoparticles with control over shape is also provided, along with a perspective on unanswered mechanistic questions in noble-metal nanoparticle synthesis and promising directions for future studies.