Electrokinetic Stacking By Microfluidic Bipolar Electrode And Nanofracture On Fused Silica Capillary

Microfluidic systems have experienced rapid growth in the past two decades due to advantages associated with miniaturization, integration, and automation. Poor detection sensitivities mainly attributed to the small dimensions and can greatly hinder their practical applications in detecting low-abundance analytes, particularly in bio-samples. Toward the goals of improvement in analytical efficiency and the detection sensitivity, many online sample preconcentration techniques based on different working principles have attracted considerable attention. Bipolar electrode focusing based on electric field gradient focusing and ion concentration polarization (ICP) based on donnan exclusion showed great potential in sample preconcentration.In the first chapter of this paper, theoretical basis of bipolar electrode focusing, and ICP at the micro-nano interface, on-column fracture for sample introduction and the applications were reviewed in the background of online sample preconcentration techniques in microchip electrophoresis.In the second chapter, polydimetholsiloxane (PDMS) injection molding, a simple and cheap fabrication method was used in the establishment of a new PDMS microfluidic bipolar electrode system by simplify traditional dual-channel BPE configuration to single-channel and single-electrode structure. In this microfluidic chip, the main factors of BPE focusing including voltage setting, background electrolyte concentration and convective flow are investigated. Anion probes were enriched under optimized conditions. The new BPE chip enriched over a hundred fold in 150 s for fluorescent probe, and 113 for λDNA in just 40 s.In the third chapter, manual preparation of a nanofracture on the fused silica capillary was presented, and the width of nanofracture is estimated by resistance measurement with a theoretical model, the width of nanofracture falled in 45-1434 nm. The relationship between fracture width and concentration polarization effect was studied with fluorescence sodium probe at the nano-fracture by fluorescence imaging. Using the fracture as the sampling unit,rhodamine 6G was found stacked due to ion concentration polarization and field amplification effect. The concentration region was postly transferred to the detection window using electroosmotic flow and detected by laser induced fluorescence (LIF). Rhodamine 6G was enriched over a hundred fold in 12 s with the nanofracture with the width of 45-300 nm.This study showed that the new BPE chip has obvious advantages of simple fabrication procedures, low cost, flexible voltage control procedures, and λDNA can also be effectively concentrated. The nanofracture could be integrated as a functional unit in the short capillary-based high speed capillary electrophoresis systems.