Nanoparticles come in all sorts of shape. Even if they are usually sketched as round objects, in reality they can be rounded or faceted according to the Platonic solids; they can be elongated or oblate, forming rod-like or disc-like objects; in certain conditions, they can be forced to assume metastable complex shapes, like tetrapods, stars, urchins, and many more.

Shape becomes a determining factor in some applications like polymer composites, where 1-D rods or fibers can be used to maximize the mechanical performance along one direction; paints and varnishes, where anisotropic optical behaviors are exploited to introduce colour effects; biochemistry, where the optical plasmonic response of a nanoparticle depends on its shape; catalysis, where certain crystalline facets present higher reactivities towards a specific process.

Not all nanoparticles are born round!