Using light patterns to manipulate self-propelled particles

Soft active matter systems, characterized by their ability to extract energy from their environment to perform mechanical work, exhibit phenomena far from equilibrium. We study a class of synthetic light activated colloidal swimmers which self-propel osmotically on a surface. Here we propose a method to manipulate the migration of the light activated colloids by carefully tuning their macroscopic environment. Through integration of a modified commercial projector with an optical microscope, we are able to shine static and dynamic light patterns onto the sample plane where the light activated swimmers live. We can use specific light patterns to set up swimmer density gradients in our sample.