Aqueous Two-Phase Systems and Microfluidics for Microscale Assays and Analytical Measurements

Abstract

Phase separation is a common occurrence in nature. Synthetic and natural polymers, salts, ionic liquids, surfactants, and biomacromolecules phase separate in water, resulting in an aqueous two-phase system (ATPS). This review discusses the properties, handling, and uses of ATPSs. These systems have been used for protein, nucleic acid, virus, and cell purification and have in recent years found new uses for small organics, polysaccharides, extracellular vesicles, and biopharmaceuticals. Analytical biochemistry applications such as quantifying protein–protein binding, probing for conformational changes, or monitoring enzyme activity have been performed with ATPSs. Not only are ATPSs biocompatible, they also retain their properties at the microscale, enabling miniaturization experiments such as droplet microfluidics, bacterial quorum sensing, multiplexed and point-of-care immunoassays, and cell patterning. ATPSs include coacervates and may find wider interest in the context of intracellular phase separation and origin of life. Recent advances in fundamental understanding and in commercial application are also considered. Expected final online publication date for the Annual Review of Analytical Chemistry, Volume 14 is August 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Size‐dependent electrophoretic motion of polystyrene particles at polyethylene glycol–dextran interfaces

“…Generally, when the PEG solution and DEX solution are mixed together, the PEG molecules and DEX molecules accumulate to different phases. It has been widely agreed that the formation of PEG-DEX aqueous two phase system (ATPS) results from the steric exclusion between the polymers [36,37]. Once the interface between the two different types of polymers forms, the diffusion of polymer molecules across the interface is limited.…”

Liquid sculpture and curing of bio-inspired polyelectrolyte aqueous two-phase systems

“…Complex coacervates, formed due to electrostatic interactions between oppositely charged polyelectrolytes, are also seen as a sub-class of ATPS, since immiscible aqueous phases are formed as well 11 – 13 . Research in ATPS have been developed rapidly, allowing for versatile applications encompassing encapsulation 14 , 15 , microfluidics 16 , wet adhesives 17 , 18 , and interfacial reactions 19 , etc.…”

Bacteria‐Inspired Aqueous‐in‐Aqueous Compartmentalization by In Situ Interfacial Biomineralization

“…[ 12–15 ] However, they are inherently thermodynamically unstable, susceptible to random fusion, making their utilization difficult. [ 16 ]…”

“…[12][13][14][15] However, they are inherently thermodynamically unstable, susceptible to random fusion, making their utilization difficult. [16] One way to prevent uncontrolled fusion is to bind these allaqueous compartments with membranous shells. For instance, by self-assembly of amphiphiles at liquid/liquid interfaces, phospholipid and polymer vesicles are extensively employed, but these synthetic vesicles without a variety of transmembrane proteins have a limit permeability, they do not permit of the in-and-out of most charged molecules and macromolecules.…”