Methods for processing droplets containing biological entities

A method of preparing a droplet containing a single pair of two biological entities, the method comprising:

• providing a first plurality of biological entities in a first fluid and providing a second plurality of biological entities in a second fluid;
• preparing a first droplet from said first fluid and preparing a second droplet from said second fluid;
• determining whether said first droplet contains a single entity of said first plurality of biological entities and whether said second droplet contains a single entity of said second plurality of biological entities;
• and
• fusing said first droplet and said second droplet which have been determined to contain a said single entity, respectively, to form a fused droplet,
• wherein the fused droplet contains the single pair of two biological entities, wherein the single pair of two biological entities comprises the single entity previously contained in the first droplet and the single entity previously contained in the second droplet such that the fused droplet allows the single entity previously contained in the first droplet to interact with the single entity previously contained in the second droplet;
• further comprising
• sorting said fused droplet from other droplets, wherein said sorting comprises detecting said droplet at a plurality of different sensor locations in a sequence on a path of the droplet along said fluid flow path;
• and
• dispensing said sorted droplet into a reservoir, wherein said dispensing comprises, after said sorting:
• selecting a fluid flow path for fluid containing the sorted droplet;
• and
• ejecting the sorted droplet from the selected path.