Abstract
Nano- and microfluidics have been a key issue for recent miniaturized flow systems. In a small confined space like microchannels, the electrostatic potential at the wall, i.e., the zeta-potential, significantly affects the flow structure and also induces electroosmotic flows under external electric fields. This paper presents fluorescence-based optical measuring techniques for the zeta-potential and fluid velocity to investigate electroosmotic flows with nonuniform zeta-potential. The evanescent wave and volume illumination are used as excitation lights for the near-wall and bulk regions, respectively. The zeta-potential is obtained imaging the near-wall fluorescent ions excited by the evanescent wave. On the other hand, the near-wall and bulk flow velocities are measured tracing the motion of submicron fluorescent particles. The spatial and temporal resolutions of velocity measurements are improved focusing on the reproducibility of laminar flows. These techniques will contribute to further development of flow systems using electrokinetics.
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