Mapping and manipulating temperature-concentration phase diagrams using microfluidics.

We describe a microfluidic device for mapping phase diagrams of aqueous samples as a function of concentration and temperature. This double-layer (poly)dimethylsiloxane (PDMS) device contains a storage layer, in which hundreds of nanolitre sized aqueous droplets can be simultaneously formed and stored. A second layer, separated by a thin, water-permeable PDMS-membrane contains twelve reservoir channels filled with different salt solutions. When there is a difference between the concentrations of salt in the reservoir solutions and the aqueous droplets, water migrates across the membrane and causes the droplets to reversibly shrink or expand and the concentration of all solutes inside the droplets changes. We now incorporate a temperature stage that generates a linear gradient in temperature across the chip oriented perpendicular to the concentration gradient. Robust operation of several variants of the PhaseChip is demonstrated with examples in liquid-liquid phase separation and protein crystallization experiments.