Nonlinear electrophoresis of point-like particles--is it possible?

A new universal method for the generation of nonlinear electrophoretic mobility of a packet of any particles is suggested. The method is based on the investigation of particle packet dynamics under the influence of an external force. The system under consideration is a homogeneous and isotropic medium with traps for these particles. Packet dynamics is described by a linear diffusion equation. The measured packet parameters are the position and the velocity of a packet maximum. It is shown that these parameters are nonlinear in the external field under definite limitations on the trap properties. This statement is proved both theoretically and experimentally for the simple model of diffusive substrate, the so-called comb structure. The prospects of designing new supporting substrates (microfluidic systems) with a nonlinear response are discussed.