Flexible and efficient eletrokinetic stacking of DNA and proteins at an HF etched porous junction on a fused silica capillary.

Better understanding of the mechanism is important for exploring the potentials of a preconcentration method. In this work, we show for the first time that the HF etched porous junction on a fused silica capillary behaves not only as a filter but also as an integrated nanofluidic interface. This junction exhibits an obvious ion concentration polarization (CP) effect, with which highly efficient electrokinetic stacking (ES) inside the capillary can be achieved without molecular size or charge type limitation. Two major types of CP based ES were proposed, and an autostop etching principle was presented for avoiding overetching. The ES can be performed in a broad range of pH and buffer concentration. Over a billion times of concentration was demonstrated by a fluorescein probe with laser induced fluorescent (LIF) detection. ES of fluorescently labeled and native DNA and protein were characterized by charge-coupled device (CCD) imaging and online capillary gel electrophoresis (CGE) with ultraviolet (UV) absorption detections, respectively. With this junction, highly efficient ES can be performed easily by voltage manipulation without any mechanical operation. We may foresee that the performance of capillary-based conventional and chip electrophoresis could be greatly enhanced with this junction in the analysis of low abundance biomolecules.