Micro-/Nanodroplets in Microfluidic Devices

Abstract

Fluid is often transported in the form of droplets in nature. From the formation of clouds to the condensation of dew on leaves, droplets are formed spontaneously in the air, on solids, and in immiscible fluids. In biological systems, droplets with lipid bilayer membranes are used to transport subnanoliter amounts of reagents between organelles, between cells, and between organs, in processes that control our day-to-day metabolic activities. The precision of such systems is self-evident and proves that droplet-based systems provide intrinsically efficient ways to perform controlled transport, reactions, and signaling. This precision and efficiency can be utilized in many lab-on-chip applications by manipulating individual droplets using microfabricated force gradients. Complex segmented flow processes involving generating, fusing, splitting, and sorting droplets have been developed to digitally control fluid volumes and concentrations to nanoliter levels. In this chapter, microfluidic techniques for manipulating droplets are reviewed and analyzed.