The authors used light to transform a colloidal soln. of spherical silver nanoparticles into larger nanoparticles of a different shape. The particle size and shape can be controlled by choosing the wavelength(s) of light used to drive the photochem. growth. These findings suggest a new way of thinking about growth of nanoparticles in soln. and show the exciting possibility that light can be used as a major control parameter in metallic nanoparticle growth reactions. [on SciFinder (R)]