1.Introduction One critical challenge in developing a portable bio-macromolecular separation device is how to design a better nanoscale channel to serve as its core component.In order to obtain a high efficiency in the purification,sorting,detection and the identification of bio-macromolecules,various channels from the 1D capillary 1,2 and 2D slit 3-10 to the 3D channel array 11 have been proposed.Particularly,using a ratchet structure to fabricate a molecular channel has been considered as a very promising solution.A ratchet channel with an asymmetric structure allows its internal colloids or molecules obtaining a net motion under external actuation.Such a net motion is sensitive to their structural specificities 12-17(such as the molecular size,length,charge and chirality).The diffusing mechanism of the macromolecules in a ratchet channel has become a critical problem in recent years.Riemann et al.15,18 reported an investigation using periodically distributed posts with alternating small and large gaps,where they found that under a biased AC electric field(consisted by an unbiased AC voltage superimposed by a DC voltage)the internal polystyrene beads showed an unexpected Absolute Negative Particle Mobility,i.e.the direction of particle transport is always the opposite of the DC voltage direction.