Detection Of Escherichia Coli O157:H7 By Selective Culture Medium And Electrochemical Methods & Fabrication Of A Hydrogen Peroxide Biosensor

The spread of diseases caused by pathogenic bacteria has become a major public health risk. In order to meet the challenges, it is critical to develop new methods for rapid and sensitive detection of pathogenic bacteria. Escherichia Coli O157:H7(E. coli O157:H7) is one of the pathogenic microorganisms. And it is also the indicator bacteria in environment measurement and food industry. Accurate and fast detection of E. coli O157:H7 is very important for human health. Herein, we designed two different methods for the detection of E. coli O157:H7. Also a novel amperometric biosensor based on multi-walled carbon nanotubes(MWCNTs), gold nanoparticles(AuNPs) and thionine was fabricated for the detection of hydrogen peroxide. In this study, the main contents are listed below:1. A selective culture medium and a novel detection method were designed for qualitative and quantitative detection of E. coli O157:H7. The main compositions of the selective culture medium are lactose, peptone, ox-gall salt, carboxymethyl cellulose, sodium chloride and potassium hydrogen phosphate, etc. During the growth of E. coli O157:H7, they can break down lactose into formic acid, lactic acid, etc, which lead to the decrease of p H in this selective medium. The concentration of E. coli O157:H7 was detected via the change of the pH. This selective culture medium was used in the detection of E. coli O157:H7 in milk. Compared with other traditional methods, this detection method with high sensitivity, simple preparation and low cost offers a promising new method for the detection of E. coli O157:H7. The result shows that detection of E. coli O157:H7 ranges from 1cfu/mL to 10000cfu/m L.2. Electrochemical biosensors are widely used in food safety and environmental monitoring due to the fact that most biosensors have excellent properties. Herein, an immunosensor based on polyaniline film and nanogold(AuNPs) was designed for the detection of E. coli O157:H7. Polyaniline film was prepared by electrochemical techniques. AuNPs was prepared by chemical synthesis. The specific antibody of E. coli was modified on Au NPs via covalent bonds. After the combination of E. coli on the electrode, electrical conductivity of the electrode decreased greatly owing to the poor conductivity of E. coli. The concentration of E. coli O157:H7 was detected via the change of differential pulse voltammetry(DPV). The result shows that detection of E. coli O157:H7 ranges from 615cfu/m L to 3342cfu/mL. Given the easy fabrication and simple detection method, the proposed immunosensor is a promising technique for effective and convenient detection of E. coli O157:H7.3. A hydrogen peroxide biosersor based on MWCNTs, AuNPs and thionine was designed. Carboxyl was introduced to the surface of MWCNTs by treating with mixed strong acid. AuNPs was modified on the electrode via electrodeposition. Images of scanning electron microscopy(SEM) show that the diameter of AuNPs is around 40 nm. Horseradish peroxidase(HRP) was covalently immobilised on the surface of AuNPs. Different concentrations of H2O2 were detected via differential pulse voltammetry(DPV). The biosensor had good stability and retained 94.1% of the initial enzyme activity after 4 weeks. It exhibited excellent electrocatalytic activity towards H2O2 with a linear range from 60?M-120?M and a detection limit of 20?M.