Study On Detection Of Bacteria Based On Dielectrophoresis And Electrical Impedance Technology

The point of care testing(POCT)of bacteria is an important goal and a big difficulty for researchers.Because of its advantages of label-free,high sensitivity and simple operation,the detection method based on electrical impedance technology is likely to reach the target of POCT.However,most studies only distinguished the sizes of the bacterial cells,and there are few studies on differentiating the shapes and death/alive of bacteria at present.In this thesis,we propose a method to detect the volume,shape and dead or alive of different bacterial cells based on electrical impedance technique.By combining with the dielectrophoresis(DEP)technique's enriching the bacterial cells,a detection technique of enriching,counting and distinguishing the bacterial cell samples was realized to achieve rapid and efficient detection and analysis of bacteria and other microorganisms.According to the aforementioned research objectives,through the theoretical studies and analysis of dielectrophoresis and electrical impedance technologies,this thesis set up a detection platform with a software and hardware system,and focused on the core sensor--microfluidic detection chip.Then we designed and optimized the microfluidic channel's structure and electrodes'distribution of the detection chip to obtain a well detection performance.By studying the fluid characteristics and micro-particles'attitude in microfluidic channel,a method of detecting and distinguishing micro-particles morphology is proposed.The chip with multistage shrinkage pipes and coplanar electrodes was designed to detect and collect electrical signal data.Using polystyrene microspheres and different shapes of SU-8 rods to simulate spherical and rod-shaped bacteria,the experiment was carried out for distinguishing them.A significant distinction(P<0.005)was obtained by using parameters of the impedance pulse width and height,and verified the effectiveness of the method very well.Then,yeast in different periods are detected and distinguished,gaining a TPR(True Positive Rate)of?0.95 with a low FPR(False Positive Rate)of?0.05.By analyzing the electrical model of cell and the theory of electrical impedance detection,the differences of electrical impedance between biological cells and microspheres,and between biological cells in different living status were achieved respectively.According to the difference of phase parameters,the differentiation(P<0.01)of alive and dead yeast was realized.The contrastive analysis of the detection of microbial survival rate by impedance flow analysis and traditional plate culture and counting showed a high correlation(correlation coefficient>0.96),which demonstrated that the impedance flow cytometry can detect microbial survival rate very well.Finally,different kinds of bacteria with similar volume were detected by the chip and distinguished by impedance parameters(P<0.01).The series of experimental results verified that the method based on impedance detection chip used in this thesis can be used to differentiate microorganism's volume,shape and death/alive,and has the advantages of high sensitivity,short experimental time and simple operation,and is hopeful to realize the point-of-care-testing of bacterial cells.