Methods and apparatus for forming 2-dimensional drop arrays

A microfluidic circuit comprising:

• a droplet forming region comprising:
• one or more channels, each having an inlet for receiving a sample and an outlet that opens into a step region;
• wherein the step region has:
• a top, a bottom, and a height greater than a height of the one or more channels;
• and
• a flat region extending from the one or more channels;
• wherein the step region is configured for finite step emulsification;
• and
• a ramp region having an angle of 10 to 80 degrees relative to the top or the bottom of the step region, wherein the ramp region terminates in an imaging region;
• wherein the imaging region is configured to collect droplets as a two-dimensional array and to provide for imaging and evaluation of the two-dimensional droplet array;
• and
• wherein the one or more channels, the step region, and the ramp region are connected such that fluid cannot flow into the imaging region from the ramp re ion without first flowing through at least one of the one or more channels.