A planar optode system based on an oxygen quenchable luminophore platinum (II) octaethyporphrin (PtOEP) bound with thin polystyrene (PS) film and UV light-emitting diodes (UV-LEDs) was developed to measure the dissolved oxygen (DO) concentration field in microscale water flows. An intensity-based method adopting a pixel-to-pixel in situ calibration technique was used to visualize DO concentration fields in a Y-shaped microchannel. The achievable spatial resolution of the acquired concentration map could be as high as 2.94 μm. The diffusion process of DO through the interface between two parallel water flows having different DO concentrations was quantitatively analyzed. We found that the thickness of the concentration gradient of DO increased as the Reynolds number decreased. The ratio of diffusion length scales coincided with the ratio of inner scales of viscous shear layers in the microchannel for two different Reynolds numbers.

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