Abstract: In a first aspect, the present invention relates to a method of producing a library of microorganisms, the method comprising the steps of: a. providing a first fluid comprising at least one single cell, b. dispersing said first fluid comprising at least one single cell in a second fluid, thereby obtaining a plurality of single-layer microfluidic droplets, wherein at least one single- layer microfluidic droplet comprises at least one single cell, wherein the second fluid is immiscible with the first fluid, c. optionally, adding to said at least one single-layer microfluidic droplet a third fluid comprising a sensing compound, wherein the third fluid is miscible with said first fluid, and wherein the third fluid is immiscible with said second fluid, d. injecting said at least one single-layer microfluidic droplet optionally comprising the sensing compound into a fourth fluid, wherein said fourth fluid is immiscible with said second fluid, thereby obtaining at least one double-layer microfluidic droplet, e.