Devices having a plurality of droplet formation regions

A device for producing droplets, the device comprising:

• a) a first channel having a first depth, a first width, a first proximal end, and a plurality of first distal ends;
• b) a second channel having a second depth, a second width, a second proximal end, and a second distal end, wherein the second channel intersects the first channel between the first proximal and first distal ends;
• c) a plurality of shelf regions, wherein each shelf region is in fluid communication with one of the plurality of first distal ends, wherein each shelf region has a width greater than the first width;
• and
• d) a collection reservoir to collect a population of droplets and comprising at least one wall forming a plurality of steps, wherein each of the steps is fluidically connected to one of the plurality of shelf regions, and wherein each step has a fourth depth that is greater than the first depth,
• e) a first liquid in the first channel;
• f) a second liquid in the collection reservoir and the plurality of shelf regions, wherein, during droplet formation, the second liquid required to form droplets is present only in the collection reservoir and the plurality of shelf regions;
• g) a third liquid in the second channel;
• and
• wherein the first and third liquids combine at the intersection of the first and second channels and form droplets in the second liquid;
• and
• wherein the first and second liquids are immiscible, and the first and third liquids are miscible.