Characterization Of A Micro-Nanofluidic Interface On Fused-Silica Capillary And Its Concentration Efficiency

With the development of microfluidics, the study on molecular transport behavior in a domain of micro-nano-scale becomes a new research field which is often termed as micro-nano-fluidics, or nanofluidics. The establishment and application of new micro-nano-fluidic system remain to be hot issues. The concentration polarization effect at the micro-nano interface is drawing more and more concerns due to its potential applications in on-line and high efficient preconcentration of charged species from small amount of samples.In the first chapter of this paper, in light of electrokinetic concentration in microchip capillary electrophoresis, theoretical basis on classical electrokinetic and electrotransport phenomena were reviewed, and the advancement of nanofluidics, particularly the conditions resulting in concentration polarization at micro-nano interface and its potential applications were summarized.In chapter Ⅱ, a micro-nano interface was established based on a well established in situ HF etching of fused silica capillary conductive. The etched capillary was further characterized by SEM. The results showed that the ion channel could be conical, and the estimated pore scale was about100nm. Ion transport through the nanopore was investigated, and ion rectification effect was noticed. Ion strength effect on the behavior of the concentration polarization was investigated by microscope fluorescence imaging. The results showed that with the increasing of ionic strength, ionic selectivity of the nanochannel would decrease.In chapter Ⅲ, the concentration efficiency of a negatively charged fluorescent probe at the interface was studied by a home made laser induced fluorescence detection system. The main influencing factors include the direction and amplitude of the transmembrane voltage and concentration time. Multiple experiments showed that charged species were effectively concentrated with the interface. In20min, as high as109times concentration was demonstrated by negatively charged fluorescein probe when the electric field was applied in the direction from outside to inside.This study showed that the micro-nano interface is highly efficient for the concentration of low concentration of charged species taking advantage of the concentration polarization effect. It is expected that this micro-nanofluidc interface will find wide applications for online concentration of charged molecules.