Nonlinear Electrophoretic Velocity of DNA in Slitlike Confinement*

We have applied zero-time-averaged alternating electric fields to DNA molecules in cross-shaped nanofluidic slits. We observed a net drift of DNA molecules, the magnitude of which depends on the square of the electric field amplitude. From the rate of accumulation of DNA at the center of the device, we derive an estimate for the second order electrophoretic mobility, μ₂. We observe that μ₂ depends on such parameters as the frequency of the alternating fields, the slit height, and DNA contour length. The observation of a nonzero μ₂ suggests that frequency dependent electrophoretic DNA separation by length is achievable with high amplitude alternating electric fields in the absence of a sieving matrix.