Nonlinear electrophoresis and focusing of macromolecules

Effects of nonlinear dependence drift velocity of (double-stranded) DNA vs. electric field strength were investigated. In comparatively weak fields, the molecular drift velocity is proportional to the external electric field, while in strong fields there is additional nonlinear component. This effect offers possibilities to manipulate the total drift velocity at will—the macromolecules of different size can be made to move in opposite directions in pulsed field gel electrophoresis. A new approach for focusing DNA molecules based on nonlinear electrophoresis and geometric trapping in electric fields is proposed. The focusing is carried out in an alternating nonuniform electric field, created by using a wedge gel with hyperbolic boundaries. It is shown that the fractions separated in such wedge retain their rectilinear shape. Gel electrophoresis experiments supported the possibility of a pronounced nonlinear focusing of DNA molecules. This nonlinear separation technique presents encouraging prospects for micromanipulating systems and also for preparative isolation of long DNA fragments and development of new separation methods for bacterial fingerprinting.