Understanding the transport details around a microparticle in confined microchannel geometry is of importance in many microfluidics-based applications such as cell/ particle manipulation and separation. Despite of numerous studies contributed in the past decade, the micro flow structure induced by the moving particle is still not quantitatively measured in experiments. In this paper, we demonstrate direct measurement of the fluid flow around a single particle traveling in a confined microchannel based on the micro particle image velocimetry technique (μPIV). In the experiments, the straight polydimethylsiloxane (PDMS) microchannel was fabricated by the standard soft-lithography technique with 100 μm height, 60 μm width and 60 mm length. The polystyrene microparticles with 20 μm diameter were employed to travel in the microchannel and induce micro flows, while smaller fluorescent particles with 1μm diameter were used as seeding particles to indicate the local velocity. After being injected in the microchnnel with water, the microparticle with 20 μm diameter quickly reached its hydrodynamic equilibrium positions, which located on the horizontal symmetry plane of the microchannel, and got captured by the μPIV system together with seeding particles. By analyzing the motion of seeding particles, the time-averaged local flow vectors, velocity fields, vortex structures and fluid streamlines were quantitatively measured under different Reynolds numbers. The proposed experimental setup can serve as a basic platform to investigate the transport phenomenon of microparticles traveling in confined flow. The quantitatively measured flow structure can also be used for model validation by other researchers.

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