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In this paper, biomolecular electropreconcentration has been demonstrated in a hybrid micro/nano-fluidic device incorporated with multi-wall-carbon-nanotubes (MWCNTs) array. Parylene (poly(p-xylylene) was deposited on MWCNTs walls as a dielectric material, the surface charge characters and density could adjusted when an induced polarizes filed was applied. The competition between electroosmotic dragging force and nonlinear electrophoretic forces induced by polarization effect is suggested responsible for the setup of two preconcentration regimes at both cathodic and anodic sides of the nanochannel. The surface charge of MCNTs is inversely proportional to the channel wall thickness and proportional to the dielectric constant of the MCNTs as well as the applied external electric-field. Electrokinetic trapping and collection can be maintained for several minutes in this device. 1 muM FITC (fluorescein) and Rhodamine B dye mixtures were easily separated by the non-neutral and neutral property of the dyes in a MCNTs filter nanochannel. A 105 folds high concentration capability of FITC-labelied IgG has been achieved in 15 min in this device which is not easily carried out by standard MEMS process. The fabrication of this charge-selsctive nanogate with direct growth of MWCNTs inside microchannel is first reported to apply to electropreconcentration.