Auto Flow-Focusing Droplet Reinjection Chip-Based Integrated Portable Droplet System (iPODs)

Droplet microfluidics provides powerful tools for biochemical applications. However, precise fluid control is usually required in the process of droplet generation and detection, which hinders droplet-based applications in point-of-care testing (POCT). Here, we present a droplet reinjection method capable of droplet distribution without precise fluid control and external pumps by which the droplets can be passively aligned and detected one by one at intervals. By further integrating the surface-wetting-based droplet generation chip, an integrated POrtable Droplet system (iPODs) is developed. The iPODs integrates multiple functions such as droplet generation, online reaction, and serial reading. Using the iPODs, monodisperse droplets can be generated at a flow rate of 800 Hz with a narrow size distribution (CV <2.2%). Droplets are kept stable, and the fluorescence signal can be significantly identified after the reaction. The spaced droplet efficiency in the reinjection chip is nearly 100%. In addition, we validate digital loop-mediated isothermal amplification (dLAMP) within 80 min with a simple operation workflow. The results show that iPODs has good linearity (R2 = 0.999) at concentrations ranging from 101 to 104 copies/mu L. Thus, the developed iPODs highlights its potential to be a portable, low-cost, and easy-to-deploy toolbox for droplet-based applications.

Automated summary

Droplet microfluidics is a powerful tool for biochemical applications, but precise fluid control is a hindrance in droplet-based point-of-care testing. This paper presents a droplet reinjection method that allows for droplet alignment and detection without precise fluid control or external pumps. By integrating a surface-wetting-based droplet generation chip, an integrated Portable Droplet system (iPODs) is developed, which can generate monodisperse droplets with a narrow size distribution and high stability. The iPODs also demonstrates good linearity in the digital loop-mediated isothermal amplification process, highlighting its potential as a portable, low-cost, and easy-to-deploy toolbox for droplet-based applications.