Electrokinetic Stacking With Nanofluidic Interface On Fused Silica Capillary And Bipolar Electrode(BPE) In PDMS Microchannel

General applicability and system miniaturization is one of the goals of microfluidic chips. However, as the decrease of a chip analytical system, great challenge arises to the sensitivity of detection means. Thus preconcentration plays substantial role in enhancing the detection capability of the existing methods. Ion concentration polarization at a micro-nano interface can be used for on-line electrokinetic preconcentration of molecule from samples of limited amount. Bipolar electrode (BPE) can also be used for electrokinetic staking using the electric field gradient locally induced by the application of a voltage across the microchannel.In the first chapter of this paper, fabrication methods of microfluidic chips, the ion concentration polarization (ICP) theory, applications of the ICP effects, direct current coupling conductivity detection and BPE focusing and its applications were reviewed.In the second chapter, ICP based concentration under two working modes in the fused silica capillary micro-nano interface was investigated by microscopic CCD imaging with fluorescein sodium. It was found that with the inside as the cathode, fluorescein sodium was enriched103times in3s; with the inside as the anode, fluorescein sodium was enriched104in30s at the boundary of the depletion region. With the contact conductivity detection means, the sample time and sample voltage was optimized, and it was found that good results were obtained with voltage800V and injection time9s. Comparing to ordinary electro injection through the micro-fracture, the detection of potassium and sodium ions were enhanced more than4000times with the ICP effect at the nanofracture. The applicability of the system was preliminary tried with a serum sample.In the third chapter, a simply microfluidic chips with embedded bipolar electrode was directly constructed in PDMS microchannel by in situ polymerication. The BPE focusing in the microchannel was clearly observed by CCD fluorescence imaging and thus become an important alternative to nanofluidic based preconcentration.This study showed that, the chip system comprised of fused silica capillary and in situ polymerization of PDMS showed good concentration efficiency for both potassium and sodium, and could be used in the analysis of complex samples such as serum. The chip BPE focusing system described in this paper is easy to establish and low cost, and more applications could be found in chip anaysis system as a functional pre-concentration unit.