A modular approach for the generation, storage, mixing, and detection of droplet libraries for high throughput screening

The desire to make microfluidic technology more accessible to the biological research community has led to the notion of "modular microfluidics'', where users can build a fluidic system using a toolkit of building blocks. This paper applies a modular approach for performing droplet-based screening, including the four integral steps of library generation, storage, mixing, and optical interrogation. Commercially available cross-junctions are used for drop generation, flexible capillary tubing for storage, and tee-junctions for serial mixing. Optical interrogation of the drops is achieved using fiber-optic detection modules which can be incorporated inline at one or more points in the system. Modularity enables the user to hand-assemble systems for functional assays or applications. Three examples are shown: (1) a "mix and read'' assay commonly used in high throughput screening (HTS); (2) generation of chemically distinct droplets using microfractionation in droplets (mu FD); and (3) in situ encapsulation and culture of eukaryotes. Using components with IDs ranging from 150 mm to 1.5 mm, this approach can accommodate drop assays with volumes ranging from 2 nL to 2 mu L, and storage densities ranging from 300 to 3000 drops per metre tubing. Generation rates are up to 200 drops per second and merging rates are up to 10 drops per second. The impact of length scale, carrier fluid viscosity, and flow rates on system performance is considered theoretically and illustratively using 2D CFD simulations. Due to its flexibility, the widespread availability of components, and some favorable material properties compared to PDMS, this approach can be a useful part of a researcher's toolkit for prototyping droplet-based assays.