(a) The figure shows a confocal fluorescence image alone (left) or merged with the corresponding brightfield image for GFP synthesized in femtoliter water-in-oil droplets. Green and grey encircled droplets represent GFP-filled and empty droplets, respectively. The graph shows the fluorescence intensity of droplets with and without (negative control) the template DNA for GFP synthesis. Scale bar: 15 μm. (b) Time courses for the synthesis of GFP in 5 differently sized droplets (1.8 fL, 5.5 fL, 13 fL, 25.5 fL, and 44.3 fL). The fluorescence of GFP reached a plateau at an earlier time (<15 min) in smaller droplets. The results represent the average data from 176 different droplets.