A system for forming a plurality of sample-containing droplets suspended in a background fluid, comprising: a planar substrate having a top surface and a bottom surface ; a sample well , a background fluid well , and a droplet outlet region selected from the group consisting of a pipette tip and a droplet well, a network of channels formed in the bottom surface of the substrate and fluidically interconnecting the sample well, the background fluid well, and the droplet outlet region; a droplet generation region defined by the network of channels and configured to generate sample-containing droplets suspended in the background fluid; and a planar sealing member forming a substantially flu id tight seal with the bottom surface of the substrate to make the network of channels fluid tight; wherein the droplet generation region is defined by the intersection of a first channel , a second channel , and a third channel ; wherein the first channel is configured to transport sample-containing fluid from the sample well to the droplet generation region , the second channel is configured to transport background fluid from the background fluid well to the droplet generation region , and the third channel is configured to transport sample-containing droplets from the droplet generation region to the droplet outlet region ; and characterized in that the sample well, the background fluid well and the droplet outlet region each comprise a well protrusion from the top surface of the substrate ; and the sample well, the background fluid well, and the droplet outlet region have been integrally formed with the substrate by injection molding; and in that the first channel has a cross-section and includes an air trap configured to prevent sample-containing fluid from being inadvertently drawn through the first channel by capillary action, wherein in the air trap the cross-section of the first channel abruptly increases in one or more dimensions. a planar substrate having a top surface and a bottom surface ; a sample well , a background fluid well , and a droplet outlet region selected from the group consisting of a pipette tip and a droplet well, a network of channels formed in the bottom surface of the substrate and fluidically interconnecting the sample well, the background fluid well, and the droplet outlet region; a droplet generation region defined by the network of channels and configured to generate sample-containing droplets suspended in the background fluid; and a planar sealing member forming a substantially flu id tight seal with the bottom surface of the substrate to make the network of channels fluid tight; wherein the droplet generation region is defined by the intersection of a first channel , a second channel , and a third channel ; wherein the first channel is configured to transport sample-containing fluid from the sample well to the droplet generation region , the second channel is configured to transport background fluid from the background fluid well to the droplet generation region , and the third channel is configured to transport sample-containing droplets from the droplet generation region to the droplet outlet region ; and characterized in that the sample well, the background fluid well and the droplet outlet region each comprise a well protrusion from the top surface of the substrate ; and the sample well, the background fluid well, and the droplet outlet region have been integrally formed with the substrate by injection molding; and in that the first channel has a cross-section and includes an air trap configured to prevent sample-containing fluid from being inadvertently drawn through the first channel by capillary action, wherein in the air trap the cross-section of the first channel abruptly increases in one or more dimensions. <EOS>