Research On Microfluidic Droplet Quantification System

Compared with traditional experimental operations,microfluidic technology greatly simplifies experimental conditions,and has the advantages of low reagent consumption,short experimental time,and high sensitivity.The droplet-based microfluidic technology uses droplets as microreactors,enabling digital manipulation of microdroplets,more flexibility,and high-throughput parallel analysis,so it is widely used in various biochemical experiments.The size and number of droplets not only represent the reagent consumption of the microreactor,but also have a complex effect on the flow resistance and flow field in the flow channel.Therefore,if the number and volume data of droplets can be detected and controlled in real time,the experimental conditions will be better controlled.The purpose of this paper is to systematically study the droplet quantification technology and design a microfluidic droplet quantification system.On the one hand,it can detect the number and volume of sample droplets in the microfluidic experiment in real time,on the other hand,the closed-loop feedback control principle is used to control the required droplet volume.The design of the system includes hardware design,software design,gas-liquid design,microfluidic electrode chip design,etc.Among them,the hardware and software design adopts a modular concept,which is composed of master,sample injection,liquid valve group,and droplet sensing modules.The sample injection module is used for reagent delivery,and the air pressure is regulated by PID algorithm.The liquid valve group module acts as a liquid circuit switch,the workflow is set by the protocol long command,and the real-time performance is guaranteed by the RTOS.The droplet sensing module is used for droplet detection and can work alone or as a feedback loop.The electrode chip uses FPC coplanar electrodes as detection electrodes,which has low cost and various detection structures.In order to explore the principle of electrode detection,capacitance model analysis and COMSOL electric field simulation were carried out on coplanar electrodes.In order to explore the influence of the electrode structure on the detection effect,coplanar electrodes with various structures were designed:two-sided electrode,finger electrode,harpoon electrode,etc.In addition,the processing of the electrode chip was investigated and explored,and two solutions to the problem of weak bonding between the PI film and PDMS were summarized: PDMS coating method and PDMS-Linker surface modification method.In terms of quantification of the number of droplets,the system can normally distinguish between droplet generation and droplet fusion events and count them.The counting accuracy rate is related to the droplet period T.It can achieve> 95% at higher fluxes(T=180 ms)and close to 100% at slower droplet rates(T=380 ms).In terms of volume quantification,two methods for detecting droplet volume based on capacitance data are summarized: peak detection method and period detection method,and compared with the results calculated by image method.The difference between peak method droplet volume detection and image method is found <15 %,the difference between the periodic method droplet volume detection and the image method is <10%,where the periodic detection method does not depend on the droplet shape parameters,and has a unique advantage for the calculation of irregular droplet volume.In addition,the detection effect of coplanar electrodes with different structures is obviously different: the bonding of the two-sided electrodes is difficult,the finger electrodes are more sensitive,but it is easy to cause signal superposition,and the harpoon electrode can meet the general experimental needs.In terms of droplet volume control,through statistical analysis of the relationship between the droplet volume and the two-phase air pressure,it was found that the air pressure value is linearly related to the droplet volume,which can achieve closed-loop feedback control of the droplet volume.This system is based on capacitive coupling detection,simple and easy to operate,and can meet the needs of miniaturization and automation of microfluidic technology.In droplet-based microfluidic experiments,this system can automatically detect and control sample droplets,greatly simplifying experimental operations.