Microfluidics Using Spatially Defined Arrays of Droplets in One, Two, and Three Dimensions

Abstract

Spatially defined arrays of droplets differ from bulk emulsions in that droplets in arrays can be indexed on the basis of one or more spatial variables to enable identification, monitoring, and addressability of individual droplets. Spatial indexing is critical in experiments with hundreds to millions of unique compartmentalized microscale processes--for example, in applications such as digital measurements of rare events in a large sample, high-throughput time-lapse studies of the contents of individual droplets, and controlled droplet-droplet interactions. This review describes approaches for spatially organizing and manipulating droplets in one-, two-, and three-dimensional structured arrays, including aspiration, laminar flow, droplet traps, the SlipChip, self-assembly, and optical or electrical fields. This review also presents techniques to analyze droplets in arrays and applications of spatially defined arrays, including time-lapse studies of chemical, enzymatic, and cellular processes, as well as further opportunities in chemical, biological, and engineering sciences, including perturbation/response experiments and personal and point-of-care diagnostics.

Recent advances in the production of controllable multiple emulsions using microfabricated devices

“…15a shows production of W/O/W emulsion drops in which two distinct aqueous drops were encapsulated within the same oil drop by integrating on the same chip one hydrophobic cross junction and one hydrophilic T-junction (Okushima et al, 2004). Drops of distinct colour and similar size were alternately formed at the hydrophobic cross-junction by injecting different aqueous streams from two opposite T inlets (Zheng et al, 2004;Pompano et al, 2011). An array of alternately arranged droplets with uniform inter-droplet spacing was carried with the oil phase to the downstream T junction, where both distinct droplets were jointly encapsulated within the same oil drop, and the latter being dispersed in the outer phase.…”

Recent developments in nucleic acid identification using solid-phase enzymatic assays

“…Microfluidic technology is also often exploited for producing spatially defined droplet arrays [84] via compartmentalization of liquids and enzymatic reaction mixtures. This is used in couple with limiting dilution technique where a sample of interest is diluted and distributed into multiple compartments in a way when the each compartment contains one or less target nucleic acid molecule.…”

Droplet‐based microfluidics for microtoxicological studies

“…Droplet numbers can exceed 10 6 in a single experimental run [28]. However, these droplets are not fixed in a certain position and therefore initial information about differences in droplet compositions disappears.…”