Research Of A Digital PCR System And Its Thermodynamic Property Analysis Based On Graphene

With the development of laboratory on a chip,microfluidic technology has been widely used in biomedical detection and chemical analysis due to its advantages of portability,precision and integration.Based on this,this paper proposes a digital PCR system based on graphene heating.A droplet flow-channel PCR amplification method was designed.The PCR reaction liquid completed the PCR amplification reaction in the form of droplet in the microchannel,which can be used to shorten the time required for digital PCR amplification.Meanwhile,a high-precision multi-channel temperature control system was developed,and graphene was used as the heating material,which could be used to improve the accuracy and reliability of the temperature control process of PCR system.A droplet digital PCR microfluidic chip was designed.The front of the chip is a Tshaped flow passage for droplet generation and the back is an amplification flow passage for PCR amplification.Since the scale of the microchannel is micron,the flow rate of PCR reaction liquid in the amplification channel is relatively large under a certain flow rate,so this design can improve the speed of PCR amplification.At the same time,a mathematical model of droplet formation was established.The relationship between the droplet relative length and the geometric parameters of the flow passage and the flow ratio of two phases was derived.Then the effects of capillary number and two-phase flow ratio on droplet formation state and droplet relative length were studied through simulation calculation,and the accuracy of droplet formation mathematical model and simulation was verified.The three-dimensional model of digital PCR chip was established,and the temperature distribution in the microchannel was simulated by COMSOL.The heat transfer model of the system was established by considering the forced convective heat transfer of the fluid inside the flow passage,the natural convective heat transfer between the microfluidic chip and the air,and the heat transfer between graphene,glass sheet and the microfluidic PDMS chip.By changing the microchannel width,the temperature distribution inside the microchannel during steady and transient processes,high temperature denaturation and annealing amplification was calculated,and the influence of microchannel width on the temperature field of digital PCR system was summarized.A high precision multichannel synchronous temperature measurement and control system was developed.Arduino software was used to program,and the resistance of PT100 thermistor was collected through the MAX31865 AD converter and converted into the temperature value.The MAX31865 AD converter was connected with the MCU through the SPI communication.Then compile the temperature control program,control the temperature at the required temperature,so as to realize the temperature measurement and control.Then the temperature measurement and control system was applied to the microfluidic PMMA chip to test and verify the accuracy of the system.The temperature control system is used to accurately measure and control the temperature during PCR amplification.An experimental platform was built to conduct experimental research on the digital PCR system,and graphene was used to heat the PCR system.By changing the width of the microchannel,digital PCR experiments were conducted for steady and transient processes,high temperature denaturation and annealing amplification,respectively,to record the value of thermistor temperature sensor,and at the same time,infrared thermography was used to shoot and record the temperature distribution in the microchannel.By comparing the results of experiment and simulation,the consistency of experiment and simulation was verified,and the method to improve the accuracy of PCR amplification temperature and the heating speed was obtained.