Abstract: Disclosed are devices, systems, kits, and methods for controlling liquid flow and, e.g., in particular, for forming droplet having substantially uniform droplet-to-droplet content. The devices, systems, and kits may include a first channel including a funnel or may include a first channel and a first-side channel, the first channel being in fluid communication with a droplet formation region. The devices, systems, and kits may further include a second channel fluidically connected to the first channel or the first side-channel. Funnels and/or side-channels may be used to enhance the control over particle spacing in the channels, thereby providing superior control over the number of particles of the same kind in formed droplets. The devices, systems, and kits of the invention may further include a mixer downstream of a channel intersection. Mixers can be used to reduce localized pockets of high concentration of dissolved ingredients.

Abstract: A sample holder includes a first member featuring a first retaining mechanism configured to retain a first substrate that includes a sample, a second member featuring a second retaining mechanism configured to retain a second substrate that includes a reagent medium, and an alignment mechanism connected to at least one of the first and second members, and configured to align the first and second members such that the sample contacts at least a portion of the reagent medium when the first and second members are aligned.