(315h) Coalescing Drops in Microfluidic Parking Networks: A Multifunctional Platform for Drop-Based Microfluidics

Automated multiwell plates and pipetting systems have revolutionized modern biological analysis. Multiwell storage allows easy barcoding for identification and retrieval of samples, and pipettes can dispense and remove known volumes of fluids into wells, allowing operations such as dilutions and washing. However, it is difficult to downscale wellplates and pipettes to manipulate fluids at the sub-microliter scale.

Droplet-based microfluidics has the potential to bring a paradigm shift in liquid handling at the sub-microliter-scale because of the ability to compartmentalize reactions in oil-isolated drops of volumes as small as picoliters. In this study, we report that a simple switch from surfactant-covered to surfactant-free drops and exploiting the coalescence between moving drop(s) and stationary drop(s) in microfluidic parking network allows (i) robust storage of arrays of monodisperse drops at prescribed coordinates, (ii) arraying of drops with gradually varying volumes in a single step, (iii) dilutions producing mondisperse droplet arrays with fine gradation in reagent concentration from drop to drop, (iv) multiplexed storage of drops of different compositions, and (v) fluid removal from static drops while retaining particles and cells. These functionalities can be achieved over a wide system parameter space, lending flexibility to our approach. We will discuss the hydrodynamic mechanisms underlying these capabilities and our method’s insensitivity to system parameters.

In summary, the functionalities delivered by our platform are akin to those provided by wellplates and pipettes, and they can be achieved using one or two pressure sources, simplifying significantly the world-to-chip interface. Thus, our simple platform is a promising inexpensive candidate for performing biological and biomedical assays with low sample/reagent volumes and parallelization capabilities.