Negative pressure-driven microfluidic mixing and photoelectric-based online detection

Conventional microfluidic mixing systems are often driven by the multiple positive pressures, which makes them suffer from the complex instrument and the potential damage to sensitive biological samples. In addition, the mixing efficiency can not be detected online. The absence of online mixing efficiency detection hinders process analysis and control, especially in scaling microfluidic devices to industrial production. To overcome these limitations, this study introduces a passive arc-shaped micromixer incorporating sharp-angled structures, driven by a negative-pressure actuation strategy. The effects of numerous parameters, including liquid flow rate, arc radius, arc angle, and the number of inlets on mixing efficiency were systematically investigated by the experiment and the numerical simulation. The results showed that a maximum mixing efficiency of ∼92% can be achieved with the simple negative pressure-driven mixing strategy. Furthermore, a new online detection method based on photoelectric sensing was developed. The correlation between mixing efficiency and the photoelectric signal is significantly influenced by the parameters including the light source intensity and the local saturation of the photodiode. Accurate online detection on the mixing efficiency was realized by optimizing these parameters to establish a stable one-to-one correspondence. The accuracy of the online detection is in good agreement with the conventional offline image detection method. With the advantages of the simple structure, easy operation, high efficiency and accurate online detection, the microfluidic chip proposed in this work would have potentials in many fields such as biomedical diagnostics, portable sensing, and precise chemical synthesis.