Researchers Develop Off-Chip Vertical Step Emulsification Droplets Preparation Device Applied for droplet digital PCR

Digital polymerase chain reaction (dPCR) is an absolute quantitative PCR reaction which can disperse the sample into numerous independent reaction units, in order to realize absolute quantitative detection in the sense of single molecule.


With increasingly mature droplet microfluidic technology, the step emulsification method has become a research direction that has attracted wide attention due to its low shear, insensitive to flow, and simple structure for easy integration. However, low throughput, high system cost and complex manufacturing process has been caused due to the limitation of microchip technology.


To develop a droplet preparation device by structural design with advantages of small volume, low cost and high throughput, a group led by Prof. WU Wenming from the Changchun Institute of Optics, Fine Mechanics and Physics of the Chinese Academy of Sciences realized an off-chip vertical step emulsification (VSE) droplet preparation device based on step emulsification method, and it is applied to droplet digital PCR (ddPCR) detection.


The VSE device consisted of a perfluoroalkoxy (PFA) capillary and a 200μL centrifuge tube. It realized the flexible change of different nozzle sizes by changing the inner diameter of different capillary tubes, and the adjustable step height through the general screw mechanism to meet the requirements of preparing droplets with different sizes.


Using the controlled variable method, by changing the sample injection speed, the inner diameter of the capillary and the height of the step one by one, the change rule of the droplet diameter under different variables was measured. The droplet diameter is in the range of between 30μm and 120μm, the coefficient of variation (CV) is less than 5%.


Finally, the droplets prepared by the VSE device were applied to ddPCR reaction. The detection results were consistent with commercial instrument (Rainsure), and the method of preparing droplets using the VSE device was easier to operate, and the throughput of droplets was higher.


In summary, the VSE device greatly reduces the difficulty of fluid control compared with traditional droplet preparation methods, and reduces the difficulty of design and manufacture of a microfluidic system. However, in the integrated application of the ddPCR system, the operation process of transferring droplets cannot be avoided, and the existence of pollution cannot be completely avoided. Therefore, the in-depth research of a simpler and easier operation scheme to the integrated ddPCR system will be further studied.

Droplet preparation process of the VSE device and result of ddPCR detection (Image by Prof. WU’s group)





Auther: SHI Bing

Changchun Institute of Optics, Fine Mechanics and Physics, Chinese Academy of Sciences

Changchun, Jilin 130033, China


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The study was published in Advanced Materials Interfaces.
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