| Electrokinetic transport in fluidic channels facilitates control and separation of ionic species. In nanometer-scale electrokinetic systems, the electric double layer thickness is comparable to characteristic channel dimensions, and this results in nonuniform velocity profiles and strong electric fields transverse to the flow. Prior work has not addressed the coupling of transverse electromigration within finite double layers and long-time (axial) electrophoretic transport of charge species.; We report analytical, numerical, and experimental studies of nanochannel electrokinetic transport and separation dynamics. We present continuum-based models for but the transport, dispersion dynamics for electrokinetic flow with finite but non-overlapping electric double layers. We also present an experimental study of transport phenomena of both charged and uncharged analytes in custom-fabricated fused silica nanochannels using quantitative epifluorescence imaging and current monitoring techniques. In these experiments, we have varied applied electric field, channel depth, background buffer concentration, and species valence to impose variations on zeta potential, effective mobility, and normalized Debye length.; Experimental results are in very good agreement with continuum-based numerical transport simulations. The models and data demonstrate that the effective mobility governing electrophoretic transport of charged species in nanochannels depends not only on bulk electrolyte mobility values, but also on zeta potential, ion valence, and background electrolyte concentration. Our results suggest new techniques for increased separation resolution of ionic species. In particular, we present a method we term "Electrokinetic Separation by Ion Valence (EKSIV)" whereby both ion valence and bulk mobility may be determined independently from a comparison of micro- and nano-scale transport measurements. Finally, we show data of size dependant mobilities for 10-100 bp DNA molecules as another example application of electrophoresis in nanochannels. |
