Microscale Determination of Aqueous Two Phase System Binodals by Droplet Dehydration in Oil

This paper analyzes the use of a dehydrating oil system to determine binodal curves of an aqueous two phase system (ATPS). Aqueous droplets containing phase-forming polymers are dehydrated at the interface between two immiscible oils. The droplets shrink due to diffusion of water into the oil phase while constantly maintaining a spherical shape. Upon sufficient dehydration, dilute one-phase solutions of phase-forming polymers separate into two phases. Comparison of the droplet diameter at this phase separation point and at the beginning allows facile calculation of the concentration of polymers that determine the binodal curve. The miniaturized droplet dehydration-based binodals obtained in this manner matched the binodals determined by the conventional diluting method but using several orders of magnitude less sample volume (150 nL droplets versus 10 mL vials).