Research On Microfluidic Detection Of Aquaculture Pathogens With Chaotically Magnetic Capture

Pathogen contamination in aquatic products exists in every process,including aquaculture,production and circulation.Foodborne diseases caused by excessive aquatic pathogens have great harm to public health,so scientific research of efficient and rapid detection of aquatic pathogens is an important means to ensure the safety of aquatic foods.However,the existing detection methods of aquatic pathogens,such as plate counting method,flow cytometry and molecular biological detection method,suffer from long detection time,difficult capture of target pathogens,large test dose and low degree of automation,which seriously restrict the improvement of the real-time detection and on-site monitoring of aquatic pathogens.Microfluidic detection of aquatic pathogens based on microfluidic chip possesses various advantages such as small consumables,fast detection speed,low detection limit and high level automation,which is the future trend of aquatic pathogens detection.In general,many kinds of pathogenic bacteria are present in the aquatic water environment,so there are two challenges in microfluidic detection for aquatic pathogens for aquatic product safety:First,How to break free of all constraints of laminar flow systems in microscale to achieve specific capture and isolation of target pathogens from the sample in the microchannel.Second,How to integrate target pathogens capture with detection for reducing errors,which achieves high-precision and high-speed detection of target pathogens in the microchannel.After correlation research of microfluidic capture and impedance detection of pathogens were summarized,this dissertation proposes a microfluidic detection method for aquaculture pathogens with chaotically magnetic capturing,and conducts theoretical and experimental explorations on the key technology.The main contributions of this dissertation are as follows:Firstly,the theoretical basis of the method is introduced,which demonstrate the theoretical feasibility for microfluidic detection for aquaculture pathogens with chaotically magnetic capturing.Secondly,the thesis analyzes the multi-physical field coupled dynamic process including magnetic field,flow field and concentration field involved in capturing pathogens in the microchannel under the oscillating magnetic field,and proves the feasibility of chaotically magnetic capturing pathogens by magnetic beads.Thus the physical model of capturing pathogens is established,and corresponding dynamic equations and boundary conditions are introduced.So the quantitative evaluation for chaotically magnetic capturing pathogens is established through numerical analysis.Thirdly,According to impedance characteristics of pathogen cells measured based on interdigitated microelectrodes,an equivalent circuit of impedance for detecting pathogens is introduced,and the sensing capacitance,double electrode layer and electrophoresis involved in the accuracy of detecting impedance are numerically simulated.Finally,In order to verify the microfluidic detection method,the dedicated microfluidic chip and magnetic field controller are designed,and based on this,An integrated experiment platform for interdigital impedance measurement of aquaculture pathogens with chaotically magnetic capturing are founded.Taked as Escherichia coli O157:H7 as an example,the detection parameters of the capture and impedance detection are optimized.The performance is compared with the standard plate colony counting method.The innovations of this dissertation are summarized as follows:1.This dissertation firstly introduces Chaos theory into microfluidic magnetic capture of aquaculture pathogens,and the particle tracking simulation is used to calculate the chaotic LE index.Through the study of chaotic motion dynamics of magnetic nanoparticles,the multi-physical field coupling numerical simulation of chaotic flow of magnetic nanoparticles in microchannels is performed.2.By multi-physics field numerical simulation coupled with magnetic field,flow field and concentration field,the dynamic analysiss of chaotic capturing process of pathogens is carried out.Simulation results indicate that the concentration of magnetic nanoparticles/pathogens complexes can be taked as the quantitative index of chaotic magnetic capture.On this basis,the chaotic capture performance is numerically analyzed,and the results showed that the method significantly improved the capture efficiency of pathogens in microscale.3.Combined with pathogen cell model and interdigital impedance sensing model on the basis of the biological structure of the pathogen cells and their arrangement between interdigital electrodes,an equivalent circuit model of microfluidic interdigital impedance sensor for pathogens is established.It is determined that the impedance detection accuracy and sensitivity of pathogens could be effectively improved by optimizing the interdigital structure and impedance scanning potential.4.A microfluidic integrated experimental platform with continuously magnetic capturing and impedance detection is fabricated.Taked as Escherichia coli O157:H7 as an example,chaotically magnetic capturing and interdigital impedance sensing of aquatic pathogens experiments are carried out on the platform respectively.The results show that compared with standard plate counting method,the capture efficiency of chaotically magnetic capturing can increase by 30%,and the detection accuracy of the method is 1.5×10~2CFU/mL,which meet the accuracy requirements for detection of aquatic food safety.This research provides a reference for the development of microfluidic integrated detection device for aquatic pathogens in the future.