Design Of A Rapid Food Pathogen Detection System

The main factor that affects our food healthy safety is caused by microorganismcontamination. The people who get bacterial food poisoning among the food poisoning accountfor more than half in total in recent years. Nowadays, the bacterial detection methods which areused by safety supervision department are still based on the traditional cell culture and standardcolony of bacteria counting. However, most conventional methods are labor-intensive andtime-consuming, often requiring24⁴8h to obtain results. In order to resolve the problems, thisthesis is supported by the Scientific Research Foundation of the Science TechnologyDepartment of Zhejiang Province-“the impedance biosensors for fast food pathogens detection（NO.2008C23011）”. A food pathogens sensor and a detection method are studied, thepreparation method for nano microbial immune sensor is proposed, and a quick testing systemon the basis of the sensor is developed.The domestic and international relevant researches of the immune sensors are summarized,and impedance measurement and nanowire preparation methods are introduced in this thesis.Based on the principle of antigen-antibody and microbial immunosensor using TiO₂nanowirebundle as sensitive material, a rapid food pathogen detection integrated system is designed andrealized. The impedance detection circuit includes a highly integrated chip AD5933to measureTiO₂nanowire bundle impedance variation with method of electrochemical impedancespectroscopy, so as to realize the rapid detection of several kinds of food pathogens. Thesoftware program and hardware circuit of the system are designed. Hardware circuit mainlyincludes serial communication module, stepper motor drive module, DC motor drive module,impedance measuring module and central control module. The software program is designed byusing the Visual Basic6.0and Keil μVision4.In this research work, some experiments are done as below:（1） Verifiability experiment: In order to confirm the binding of the target bacteria onto thesurface of antibody modified nanowire, the TiO₂nanowire bundle used in the experiment isexamined with scanning electron microscopy. We can see that the TiO₂nanowires can capture the Escherichia coli of about2.0μm. This shows that the design principle of the sensor isfeasible.（2） Effective experiment: Before and after injecting the Escherichia coli, the sensor istested. According to this experiment, the system can detect the existence of Escherichia coli andthe test period costs about50minutes. The experimental results indicate that the system is fastand effective.（3） Repeatability experiment: On the condition of the same concentration Escherichia coli,the sensor is tested3times. The experimental results show that the sensor has a quite goodrepeatability in the frequency range of1kHz to10kHz.（4） Sensibility experiment: Six kinds of different concentrations of Escherichia coli areassayed with the Dot Blot analysis method and homemade detection system respectively. Thefunction relationship is established between the amount of Escherichia coli and impedancevalue. The experimental results indicate that the system can detect as low as4.5×10²cfu/mL ofEscherichia coli.