Fig. 1: Colloidal transport in light-induced activity gradients.
From: Colloidal transport by light induced gradients of active pressure
a We project patterns of green light to modulate bacterial activity around colloidal particles. A modulation disc of radius R is centered on each particle and divided into two halves with light intensity values I− < I+ and corresponding velocities v− < v+. Outside these modulation disks we set a uniform background of intensity I0 corresponding to a mean speed v0. The position of these disks is continuously updated to follow particle positions. b A sample snapshot of the system taken using dark-field microscopy shows several colloidal beads and their trajectories (in green). When illuminated with the structured pattern in a, bacteria accumulate in the slow side and the colloidal beads drift systematically in the direction pointing towards the fast side. c A magnified view of the box shown in b. Parameters: R = 40 μm, I− = 0.1 mW/mm2, I0 = 0.7 mW/mm2, I+ = 0.9 mW/mm2. Scale bars are 50 μm.
