A method of generating deformable gel beads that contain a single colloidal particle is described. Gel beads containing a particle are isolated from those that do not contain a particle, based on differences between the buoyant density of these gel bead populations. The gel beads containing a particle are subsequently co-encapsulated at a high efficiency into droplets that can comprise additional objects such as cells, other particles, or reagents. The gel coating on the rigid particle prevents clogging in narrow channels, such as those of a droplet generator.