Numerical Simulation and Experimental Verification of Droplet Generation in Microfluidic Digital PCR Chip

Microdroplet PCR in Microfluidic Chip Based on Constant Pressure Regulation

A device and method for the constant pressure regulation of microdroplet PCR in microfluidic chips are developed to optimize for the microdroplet movement, fragmentation, and bubble generation in microfluidic chips. In the developed device, an air source device is adopted to regulate the pressure in the chip, such that microdroplet generation and PCR amplification without bubbles can be achieved. In 3 min, the sample in 20 μL will be distributed into nearly 50,000 water-in-oil droplets exhibiting a diameter of about 87 μm, and the microdroplet will be subjected to a close arrangement in the chip without air bubbles. The device and chip are adopted to quantitatively detect human genes. As indicated by the experimental results, a good linear relationship exists between the detection signal and DNA concentration ranging from 10¹ to 10⁵ copies/μL (R² = 0.999). The microdroplet PCR devices based on constant pressure regulation chips exhibit a wide variety of advantages (e.g., achieving high pollution resistance, microdroplet fragmentation and integration avoidance, reducing human interference, and standardizing results). Thus, microdroplet PCR devices based on constant pressure regulation chips have promising applications for nucleic acid quantification.

Image Segmentation and Quantification of Droplet dPCR Based on Thermal Bubble Printing Technology

Thermal inkjet printing can generate more than 300,000 droplets of picoliter scale within one second stably, and the image analysis workflow is used to quantify the positive and negative values of the droplets. In this paper, the SimpleBlobDetector detection algorithm is used to identify and localize droplets with a volume of 24 pL in bright field images and suppress bright spots and scratches when performing droplet location identification. The polynomial surface fitting of the pixel grayscale value of the fluorescence channel image can effectively compensate and correct the image vignetting caused by the optical path, and the compensated fluorescence image can accurately classify positive and negative droplets by the k-means clustering algorithm. 20 µL of the sample solution in the result reading chip can produce more than 100,000 effective droplets. The effective droplet identification correct rate of 20 images of random statistical samples can reach more than 99% and the classification accuracy of positive and negative droplets can reach more than 98% on average. This paper overcomes the problem of effectively classifying positive and negative droplets caused by the poor image quality of photographed picolitre ddPCR droplets caused by optical hardware limitations.

Micro-injection Molded Droplet Generation System for Digital PCR Application

Sensitive, effective, and quantitative analysis of infectious pathogens is an important task for the prevention of human health threats. Herein, we present an advanced approach to producing gene-encapsulated microdroplets for quantitative analysis using a micropatterned metal mold and injection molding technique with an automatically operated system. An injection molded microdroplet generation device was successfully fabricated with a minimum channel width of 30 μm and optimized to produce 100 μm diameter droplets. The optimized microchannel design and flow rate also enable the production of stable numbers of microdroplets (~ 16,000 droplets). To verify the applicability of our device and system to droplet-based digital PCR analysis, Escherichia coli (E. coli) O157:H7 was selected as a model bacterial pathogen, and the stx2 gene was amplified in the microdroplets. The generated microdroplets exhibit both chemical and mechanical stability, and our results are similar to those obtained by a commercially available method. Accordingly, the usefulness of the microdroplet generative device and system is confirmed as a simple, fast, and reliable tool for the quantitative molecular analysis of infectious diseases.