Modeling And Simulation Of Microfluidic Chip For Nucleic Acid Detection

With the development of integration,automation and miniaturization of micro-analysis systems,microfluidic chips have been gained widespread attention in the fields of disease diagnosis,biochemical analysis and clinical detection.Microfluidic chip is one of the effective ways to realize integration of micro-analysis system,which is to complete the basic operation unit of sample preparation,reaction,separation,detection and so on through integration of different functional chips,and automatically completes the whole process of analysis.Microfluidic chip technology has shown strong application prospects in nucleic acid detection.The main functions of microfluidic chip for nucleic acid detection are micromixing and magnetic beads capture.The mixing efficiency of solution and magnetic beads capture can improve detection accuracy of microfluidic chip.In this paper,the microfluidic chip for nucleic acid detection developed by the laboratory is optimized for micromixing and nucleic acid extraction unit.The numerical simulation method of computational fluid dynamics(CFD)is used to perform finite element analysis of influencing factors of flow filed distribution,solution mixing mechanism and magnetophoresis separation in microchannels.Firstly,two-dimensional dynamic model of the micromixer was established according to the theory of fluid dynamics and convection diffusion.The micromixer is numerically simulated using COMSOL Multiphysics to analyze the influence of velocity,diffusion coefficient and other parameters on the mixing.The pulse type and built-in block type micromixer improve the mixing effect by changing mixing mode.According to the principle of magnetophoresis separation analysis force and motion equation of magnetic beads,and establish the interaction magnetic field and flow field under the action of two-dimensional dynamic numerical model of magnetic beads.The flow field and magnetic field model are numerically simulated to obtain the motion characteristics of the magnetic beads under different magnetic field distributions and influence of residual flux density,inlet velocity and magnetic susceptibility on the magnetic beads capture rate.By numerical simulation of microfluidic chip for nucleic acid detection is adopted to obtain the influencing factors of fluid mixing and magnetic beads capture rate.The conclusions are as follows:(1)T-type straight channel micromixer uses solution diffusion to mixing.When the flow rate u=0.5mm/s,the flow rate per unit time is large and solution is completely mixed,and the mixing effect is the best.For the pulsed micro-mixer,when the inlet flow rate is 200mm/s,the diffusion coefficient is greater than 5e-10m~2/s,and P/W=1,the mixing effect of the pulsed micro-mixer is the best.For the built-in block-type micromixer,the effects of obstacle height change on the mixing effect of micro-mixer are simulated when the diffusion coefficient is 1e-9m/s,the width of micro-channel is50um,the width of blocking block is 20um and the inlet velocity is 0.05mm/s,5mm/s and 500mm/s,respectively.The simulation results show that the optimal hybrid model of the built-in block-type micro-mixer is a micro-mixer with obstacle height h1=10?m and h2=80?m.The micro-mixer can achieve high-efficiency mixing at high speed.(2)The results of magnetic beads capture show that magnetic flux density and uniformity inside magnets are proportional to aspect ratio h/w of magnets.When h/w is increased from 0.5 to 6,the capture rate of magnets with the same polarity ranges from twenty-six point seven percent to one hundred percent;The maximum capture rate about magnetic beads of opposite polarity magnets and single magnet are sixty-three point three percent and fifty-three point three percent,respectively.Effect of magnetization direction of double magnets on the capture rate is when aspect ratio h/w is less than 2,capture rate of magnetic beads with opposite polarities is higher,which will less than the same polarity magnetic capture rate contrarily.When inlet flow rate is between 1mm/s and 2cm/s,magnetic beads capture rate decreases with increasing of velocity by simulation calculation.And magnetic beads capture rate increases with the increase of residual flux density and magnetic beads susceptibility.The simulation results can guide the optimal design of microfluidic chip for nucleic acid detection.and be used in nucleic acid detection experiments to guide the mixing of solutions and optimize the use of magnetic beads,so as to improve the efficiency of microfluidic chip for detection of nucleic acid-related diseases.