# Design and research of a passively mixed microfluidic chip for copper ion detection

## TL;DR

This paper introduces a high-performance microfluidic chip that improves mixing efficiency for detecting copper ions using passive design features.

## Contribution

The novel contribution is a microfluidic chip with variable cross-sectional channels and passive mixing structures that achieve high mixing efficiency.

## Key findings

- The chip achieved a mass fraction mixing index of 0.9998 at a Reynolds number of 0.5.
- The pressure drop was only 0.1502 Pa, outperforming similar chips.
- The mixed solution detection value was 101.99% of the completely mixed solution.

## Abstract

At the micro-scale channel dimensions and relatively low Reynolds numbers, fluids can only mix through diffusion in a laminar flow state. This dependence on molecular diffusion significantly hinders the mixing performance of microfluidic chips. To address this issue and promote the application of microfluidic technology in the detection of heavy metal ions, we propose a high-performance microfluidic chip with variable cross-sectional channels based on passive mixing. By setting bias centrifugal bends and linear flow channels with periodic diameter changes, the mixing efficiency of the microfluidic chip has been significantly improved. To verify the theoretical mixing effect, we set up eight groups of different Reynolds number conditions for the microfluidic chip and simulated the fluid flow in laminar state. Through analyzing the simulation cloud diagrams and the mass fraction mixing index, it was found that when the Reynolds number was 0.5, the mixing efficiency of the microfluidic chip reached the optimal state, with a mass fraction mixing index of 0.9998, and the pressure drop was only 0.1502 Pa, which was higher than the mixing efficiency of similar chips under the same conditions. Using 3D printing technology to fabricate the microfluidic chip and conducting characterization analysis. To verify the actual mixing effect, a colorimetric mixing experiment was set up, and a visual mixing effect analysis of the chip was conducted. Through ICP-MS for copper ion detection experiments, three control experiments were set up to conduct a data-driven mixed effect comparison analysis of the chip. After verification, the overall and local mixing effects of the microfluidic chip were highly consistent with the simulation results under the same conditions, and the detection value of the mixed solution was 101.99% of the completely mixed solution, showing good consistency. Therefore, this chip has excellent mixing performance and is conducive to promoting the application of passive microfluidic chips in fields such as heavy metal detection.