Living Crystals of Light-Activated Colloidal Surfers

Abstract

Light On Clusters From schools of fish to bacterial colonies, large-scale phenomena—such as swarming or pattern formation—are ubiquitous. In such systems, there is a continuing question as to the relative importance of "intelligence" (biology) of the agents versus purely physical effects. Working with synthetic colloids, Palacci et al. (p. 936 ) show that self-organized clustering can be switched on and off to form crystals that dissolve when the light source is turned off. The particles consist of a hematite cube partly encapsulated in a polymeric sphere that is able to catalyze chemical reactions when exposed to light. The self-assembly behavior results from a combination of propelling forces, osmotic effects, and coupling between colloidal and tracer particles.