Electropreconcentration with charge-selective nanochannels.

We report on the systematic investigation of electropreconcentration phenomena in hybrid micro/nanofluidic devices. The competition between the electroosmotic dragging force and the highly nonlinear electrophoretic forces induced by the polarization effect is responsible for four preconcentration regimes within such structures that can arise at both cathodic and anodic sides of the nanochannel. Numerical calculations on the spatiotemporal concentration of charged molecules confirm such a classification, showing a general agreement with the reported experimental data at low and moderate ionic strengths. The results also suggest that both the mobility and the valence of the species of interest are important parameters in the determination of the preconcentration rates.