The generation of droplets is one of the most critical steps in the droplet digital polymerase chain reaction (ddPCR) procedure. In this study, the mechanism of droplet formation in microchannel structure and factors affecting droplet formation were studied. The physical field of laminar two-phase flow level was used to simulate the process of droplet generation through microfluidic technology. The effect of the parameters including flow rate, surface tension, and viscosity on the generated droplet size were evaluated by the simulation. After that, the microfluidic chip that has the same dimension as the simulation was then, fabricated and evaluated. The chip was made by conventional SU-8 photolithography and injection molding. The accuracy of the simulation was validated by comparing the generated droplets in the real scenario with the simulation result. The relative error (RE) between experimentally measured droplet diameter and simulation results under different flow rate, viscosity, surface tension and contact angle was found less than 3.5%, 1.8%, 1.4%, and 1.2%, respectively. Besides, the coefficient of variation (CV) of the droplet diameter was less than 1%, which indicates the experimental droplet generation was of high stability and reliability. This study provides not only fundamental information for the design and experiment of droplet generation by microfluidic technology but also a reliable and efficient investigation method in the ddPCR field.

With the continuous impact of COVID-19, the demand for rapid genetic diagnosing at the inspection and quarantine site, emergency treatment of sudden infectious diseases and clinical in vitro diagnosis was increasing rapidly. In order to achieve rapid, automatic nucleic acid extraction and detection, an automatic diagnostic system which integrates nucleic acid extraction, amplification and biochip fluorescence detection is designed. The diagnostic system designed based on multidisciplinary intersection of biology, optoelectronics, machinery and computer technology. At first, the nucleic acid extraction part has 1-8 sample flux and uses the principle of the silicon filter can adsorb nucleic acid at different pH to achieve nucleic acid extraction. After the extraction process, the nucleic acid is injected into biochip through robotic arm. There is a specific microarray reaction chamber on the chip, which can be combined with a specific biological substance; Secondly the amplification part used the principle of flat-plate PCR to achieve nucleic acid amplification in the biochip; After amplification, the nucleic acid detection realized under the irradiation of the excitation light at 530nm, the specificity target on the biochip will emit light, thus the fluorescence image scanned by COMS camera and the result analyzed by the software on PC; At last device control, automation and detection of the integrated device realized by the STM32 single-chip microcomputer and CAN communication method to establish a device communication network. The diagnostic system will automate workflow, and provides a result that reports on the detection and interpretation of targets in the samples. The imaging module resolution was less than 10 microns/pixel. The CV value of the sample was less than 10%. The results provide that the diagnostic system can provide more accurate and more automated equipment for nucleic acid extraction, amplification and detection.