title: Thermal separation: interplay between the Soret effect and entropic force gradient.
abstract: Thermophoresis, the Soret effect, depletes a high concentration of a polyethylene glycol polymer solution from the hot region and builds a concentration gradient. In such a solution, solutes of small concentration experience thermophoresis and polyethylene glycol concentration-dependent restoring forces. We report that by using focused laser heating and varying the polyethylene glycol concentration one observes geometrical localizations of solutes like DNA and RNA into patterns such as a ring. For DNA up to 5.6 kbp, the ring size decreases following a behavior analogous to a gel electrophoresis separation. Above 5.6 kbp, the ring diameter increases with the DNA length. Mixtures of DNA and RNA can be separated as well as different RNA lengths. Separation of colloids is also observed. The experiments might be relevant for the separation of small RNA ribozymes in an early stage of life.
authors.affiliation: Center for Studies in Physics and Biology, The Rockefeller University, New York, New York 10021, USA.
authors.forename: Yusuke T
authors.initials: YT
authors.lastname: Maeda
authors.forename: Axel
authors.initials: A
authors.lastname: Buguin
authors.forename: Albert
authors.initials: A
authors.lastname: Libchaber