Aqueous two-phase systems (ATPS) are made from a mixture water and two different solutes that separate into two aqueous layers at certain solute concentrations. ATPS have many useful applications including sewage treatment, separation of metals, and understanding primitive and modern-day cells. Despite the utility and potential importance of ATPS, the separation of these layers is still not well understood, especially on the molecular level. Herein, we explore a dextran/PEG ATPS system and use fluorescence polarization as a means to detect changes in motion of the solutes upon separation. Fluorescence polarization is sensitive to changes in the tumbling rate of fluorescent molecules and here, fluorescently labeled dextran was the main reporter of these molecular motions. We observed changes in polarization within the dextran-rich layer upon the formation of the ATPS that was not observed for an aqueous dextran solution at much higher concentrations than what was in the ATPS. This spectroscopic change indicates fluorescence polarization to be an appropriate technique for exploring molecular motion and ordering within ATPS systems. Further work is also being performed that will allow for the observation of fluorescently labeled PEG within the PEG-rich later, which may provide further insight to the molecular processes relevant for the formation of these two aqueous layers.

Observing solvent ordering within aqueous two-phase systems using fluorescence polarization

ACS Spring 2022

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