Studies On Microfluidic Chips Of Droplet Generation And Detection For Digital PCR

Microdroplet technology is a novel method of fluid manipulation based on Microfluidics that controls droplets with tiny liquid volume. The droplet unit functions as a micro-reactor, which greatly highlights the advantages of microfluidic chip such as high sensitivity, low consumption, high throughput detection and high automation. The droplets have many advantages, such as good dispersion, small size, no cross contamination, stable production rate and stable reaction conditions. It will be much easier for droplet-based PCR reaction system to achieve small-volume and high-throughput analysis. Droplet technology can greatly improve the reaction efficiency of traditional digital PCR thus it will simplify its analysis process, which has significant meanings in high-throughput analysis.In this paper, we have designed microdroplet generation and detection chips. Microdroplet generation chips can generate droplets in a fast, uniform and stable way. Droplet diameter is approximate 0.1mm and the generation rate is about 1500 per second. Gathering these droplets and sample’s PCR amplification will take place in these droplets. After that, microdroplet detection chips will arrange these droplets in sequence and the distance between droplets is 1mm. Then these droplets pass through flow cytometry detection system, and we can achieve rapid and accurate detection of the amplification results, the detection rate of droplets is 200 per second.The main work and achievements are as follows:1. We use COMSOL Multiphysics software to achieve the simulation of droplet generation and detection module. The channel’s structure, boundary conditions, negative pressure and other factors’ impacts on the droplets’ size, generation rate and spacing is discussed. According to the simulation results, we have specified droplet’s technical requirements and designed the geometry of microdroplet chips so that the droplets can fulfill the reaction and detection requirements of digital PCR system.2. Through research of the processing technology of SU-8 photoresist, we have produced the desired structure of SU-8. Then, we use PDMS micromolding and bonding techniques to get the microfluidic chip. The chip have many advantages, such as high bonding strength, smooth surface and good hydrophobic properties. The chip we designed can fulfill the needs of digital PCR reaction and detection systems.3. In this paper, a negative pressure system was introduced to drive droplet’s motion. We studied the relationship between microfluidics’ friction and flow distance within microchannel. Then, by applying the friction loss theory, we get the desired negative pressure driving force. Finally, the droplets’ uniformity was analyzed.Conclusion:1. By using scanning electron microscope(SEM), the structure of microfluidic chip was observed and measured. Microchannel has good steep property and depth consistency. Its depth is about 100 μm. Besides, its surface smoothness is great. The tolerance of microstructure’s height and width can be controlled within 10 μm. Measurement results show that the chips fabricated by MEMS process can fully meet the design requirements.2. By using high-speed camera(10000 frame/sec), we carry out droplet experiments of droplet generation and detection chip. Droplets generationrate and detection rate can be obtained through counting analysis. And we obtain the distance of adjacent droplet and droplet diameter through graphical comparison. Experiments show that droplet generation and detection chip we made can fulfill the needs of digital PCR system.