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Updated: Feb 2, 2026

The Diffusion of Passive Tracers in Laminar Shear Flow
Published on: May 1, 2018
A Diffusion-Based pH Regulator in Laminar Flows with Smartphone-Based Colorimetric Analysis
1ASIC and System State Key Laboratory, School of Microelectronics, Fudan University, Shanghai 200433, China. 14110720019@fudan.edu.cn.
Abstract:
A strategy for an on-chip pH regulator is demonstrated computationally and experimentally, based on the diffusion characteristics of aqueous ionic solutions. Micro-flows with specific pH values are formed based on the diffusion behaviors of hydrogen and hydroxide ions in laminar flows. The final achieved pH value and its gradient in the channel can be regulated by the amount of ions transported between laminar flows, and the experimental results can be further generalized based on the normalized Nernst-Planck equation. A smartphone was applied as an image capture and analysis instrument to quantify pH values of liquids in a colorimetric detection process, with monotonic response range of ~1⁻13.
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