Size-dependent detachment of DNA molecules from liquid–liquid interfaces

Binary aqueous solutions of poly(ethylene glycol) (PEG) and dextran form two phases with a liquid–liquid interface at which DNA molecules can be accumulated using an electric field. Studying DNA strands of different lengths reveals that the interface acts as a size-selective filter for molecules. Upon increasing the electric field strength, the small molecules are first detached from the interface, followed by the larger ones. Besides the contributions to a better understanding of the interaction of nanoscopic objects with liquid–liquid interfaces, the work demonstrates novel pathways for the size separation of DNA. We anticipate that by optimizing the parameters governing the detachment of molecules or nanoparticles, superior schemes for DNA separation or concepts of functional liquid interfaces could emerge.