Figure 1. Microfluidic devices and digital RT-PCR workflow used in this study.

(A) Drops containing RNA and RT-PCR reagents are created with a microfluidic T-junction and carrier oil. Brightfield microscopy images of the drop formation are shown below, the middle image showing the generation of one population of drops from a single reaction mixture, and the lower the generation of two populations from two mixtures. The red arrows indicate the direction of emulsion flow in the illustrations. (B) After formation, the drops are picoinjected with reverse transcriptase using a picoinjection channel triggered by an electric field, applied by an electrode channel immediately opposite the picoinjector. Picoinjection fluid is pictured as dark gray in the schematic diagram. (C) The picoinjected drops are collected into a tube, thermocycled, and imaged with a fluorescent microscope.