Devices, systems, and kits for forming droplets

1. 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 first distal end;

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 shelf region in fluid communication with the first distal end and having a third depth and a third width, wherein the third width is greater than the first width; and

d) a step region having a wall having a depth greater than the first and third depths, wherein the shelf region is fluidically connected to the step region, and the shelf region is disposed between the first distal end and the step region,

wherein a first liquid flowing from the first distal end and a third liquid flowing from the second distal end combine and form droplets in a second, immiscible liquid at the step region.

2. The device of claim 1 , wherein the third width increases from the first distal end to the step region.

3. The device of claim 1 , further comprising a first reservoir in fluid communication with the first proximal end.

4. The device of claim 1 , further comprising a second reservoir in fluid communication with the second proximal end.

5. The device of claim 1 , further comprising a collection reservoir in fluid communication with the step region.

6. The device of claim 1 , wherein at least one of the first channel or the second channel further comprises a groove.

7. The device of claim 1 , further comprising a third channel having a third proximal end and a third distal end, wherein the third proximal end is in fluid communication with the shelf region, and wherein the third distal end is in fluid communication with the step region.

8. A system for producing droplets, the system comprising:

a) a device for producing droplets, the device comprising:

i) a first channel having a first depth, a first width, a first proximal end, and a first distal end;

ii) 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;

iii) a shelf region in fluid communication with the first distal end and having a third depth and a third width, wherein the third width is greater than the first width; and

iv) a step region having a wall having a depth greater than the first and third depths, wherein the shelf region is fluidically connected to the step region, and the shelf region is disposed between the first distal end and the step region;

v) a first reservoir in fluid communication with the first proximal end, wherein the first reservoir comprises a first liquid; and

vi) a second reservoir in fluid communication with the second proximal end, wherein the second reservoir comprises a third liquid, wherein the first and third liquids are miscible with each other and wherein the first and third liquids combine at the intersection of the first channel and second channel,

b) a second liquid contained in the shelf and step regions, wherein the first liquid and the second liquid are immiscible with each other,

wherein the combined first and third liquids, flowing from the first distal end to the step region, form droplets of the combined first and third liquids dispersed in the second liquid.

9. The system of claim 8 , wherein the first liquid comprises particles.

10. The system of claim 8 , wherein the third liquid comprises an analyte.

11. The system of claim 8 , wherein the third width increases from the first distal end to the step region.

12. The system of claim 8 , further comprising a collection reservoir in fluid communication with the step region.

13. The system of claim 8 , wherein the device further comprises a third channel having a third proximal end and a third distal end, wherein the third proximal end is in fluid communication with the shelf region, and wherein the third distal end is in fluid communication with the step region.

14. A kit for producing droplets, the kit comprising:

a) a device for producing droplets, the device comprising:

i) a first channel having a first depth, a first width, a first proximal end, and a first distal end;

ii) 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;

iii) a shelf region in fluid communication with the first distal end and having a third depth and a third width, wherein the third width is greater than the first width; and

iv) a step region having a wall having a depth greater than the first and third depths, wherein the shelf region is fluidically connected to the step region, and the shelf region is disposed between the first distal end and the step region,

v) a first reservoir in fluid communication with the first proximal end; and

vi) a second reservoir in fluid communication with the second proximal end,

b) a first liquid in a reservoir;

c) a second liquid in a reservoir, wherein the first liquid and the second liquid are immiscible with each other,

wherein the first liquid flowing from the first distal end forms droplets in the second, immiscible liquid at the step region.

15. The kit of claim 14 , wherein the first liquid comprises particles.

16. The kit of claim 14 , wherein the third width increases from the first distal end to the step region.

17. The kit of claim 14 , wherein the device further comprises a collection reservoir in fluid communication with the step region.

18. The kit of claim 14 , wherein the device further comprises a third channel having a third proximal end and a third distal end, wherein the third proximal end is in fluid communication with the shelf region, and wherein the third distal end is in fluid communication with the step region.