Electropreconcentration diagrams to optimize molecular enrichment with low counter pressure in a nanofluidic device
Résumé
Ion-concentration-polarization (ICP) - based focusing electrokinetics nanofluidic devices have been developed in order to simultaneously detect and enrich very diluted analytes on chip. However, stabilization of focal points over long time under the application of the electric field remains as a technical bottleneck. If pressure-assisted preconcentration methods have been proposed to stabilize propagating modes at 1⁄Du ≪1, these recent protocols remain laborious for optimizing experimental parameters. We report “field/pressure” E/P diagrams for fluorescein where the typical regimes, i.e. propagating focusing, stable focusing and stacking can be observed. The region of stable focusing is shown to vary depending of the nanoslit length (100µm < Lnanoslit < 500µm) and the nature of the background electrolyte (BGE) (KCl and NaCl). Longer nanoslits (500µm) produce stabilization at low pressure, whereas NaCl BGE offers a narrower and more fluorescent stable window in the E/P diagram compared to KCl. Finally, the ability of such pressure-assisted protocol to concentrate negatively charged proteins has been tested with 10µM ovalbumin in HEPES and the corresponding E/P diagram for ovalbumin confirms the existence of a stable focusing regime at low electric field.
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