Disclosed herein are embodiments of gold nanoparticles and methods of making and using the gold nanoparticles. The disclosed gold nanoparticles have core sizes and polydispersities controlled by the methods of making the gold nanoparticles. In some embodiments, the methods of making the gold nanoparticles can concern using flow reactors and reaction conditions controlled to make gold nanoparticles having a desired core size. The gold nanoparticles disclosed herein also comprise various ligands that can be used to facilitate the use of the gold nanoparticles in a variety of applications.