Investigation of co-flow step emulsification (CFSE) microfluidic device and its applications in digital polymerase chain reaction (ddPCR)

The co-flow step emulsification (CFSE) is very sensitive to the two-phase fluid interfaces, we conjecture that the CFSE hydrodynamic model depends on several key factors and the droplet generation process can be precisely controlled, thus to obtain droplet emulsions with the "ultra-high volume fraction of inner-phase" and "flexible droplet size" characteristics. The resulting droplets are expected to be applied to droplet digital PCR (ddPCR) with "high information density" and "wide dynamic range" advances. By combining numerical simulation and fluid dynamics experiments, we have investigated the crucial parameters affecting the CFSE two-phase interface and finally achieved the prediction and guidance for CFSE droplet production. With the help of the CFSE device, multivolume droplet populations were produced on demand. Then, ddPCR tests were performed with DNA concentrations from 10 copies/μL to 20,000 copies/μL. The CFSE device owns an ultra-wide dynamic range (up to 5 orders of magnitude), showing excellent quantification ability of nucleic acid targets.