The present disclosure, among other things, provides new technologies for preparation of anisotropic nanoparticle cores (e.g., anisotropic gold nanoparticle cores) and compositions thereof. Provided technologies show a number of advantages as compared with previously available options for preparing anisotropic nanoparticle cores, including, for example, that they typically utilize mild reaction conditions and, in many embodiments, only environmentally benign agents. The present invention therefore provides "green" nanoparticle technologies. Surprisingly, in many cases, the same set of reactants can be used, under modestly different conditions, to generate nanoparticle cores of different shapes. The present invention provides selection rules for reaction conditions that generate populations containing particular shapes of interest.
