| An electrochemical DNA biosensor is a biosensor that is used for analyzing or detecting DNA with the electrochemical method. Due to its advantages such as cheap device, fast response, high sensitivity and good selectivity, electrochemical DNA biosensor has attracted considerable interests. It is not only used for recognizing specific DNA sequences but also for investigating the interaction of DNA with drugs and chemical pollutants and the DNA damage. Otherwise, it has also been widely used in the design and synthesis of specific drugs, clinical diagnosis, in vitro drug screening and environmental monitoring. Owing to the small size effect, quantum size effects and surface effects resulting from its unique structure, nano-material has shown distinctive function in many fields such as optical, electronic, adsorption, catalysis and so on. In our work, nano-materials were used to modify the electrode and two new electrochemical DNA biosensors were prepared and used for detecting DNA damage. Based on the oxidation signal of guanine, DNA damage induced by bisphenol A, acrylamide and its metabolites were directly detected without any other external indicator.The dissertation is divided into two main parts as follows:(1) A glassy carbon electrode was modified with dsDNA and a nanocomposite composed of multi-walled carbon nanotubes and Chitosan (MWNT-Chit). The electrode was applied to the electrochemical detection of DNA damage as induced by in situ generated bisphenol A (BPA) radicals through electro-oxidation. The modified electrode was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The results indicate that MWNT-Chit nanocomposite represents a viable platform for the immobilization of DNA that effectively promotes electron transfer between DNA and the electrode. The mode of interaction between DNA and BPA was investigated by differential pulse voltammetry and UV-vis spectrophotometry, indicating that the dominant interaction is intercalation. In order to explore the mechanism of damage caused by BPA radicals, the electro-oxidation of BPA at the modified glass electrode was investigated. Based on the signal for guanine without any other external indicator, DNA damage was investigated through the electro-oxidation of BPA.(2) A new electrochemical biosensor for directly detecting DNA damage induced by acrylamide (AA) and its metabolite was presented in this work. The graphene-ionic liquid-Nafion modified pyrolytic graphite electrode (PGE) was prepared, and then horseradish peroxidase (HRP) and natural double-stranded DNA were alternately assembled on the modified electrode by the layer-by-layer method. The PGE/graphene-ionic liquid-Nafion and the construction of the (HRP/DNA)n film were characterized by electrochemical impedance spectroscopy. With the guanine signal in DNA as an indicator, the damage of DNA was detected by differential pulse voltammetry after PGE/graphene-ionic liquid-Nafion/(HRP/DNA)n was incubated in AA solution or AA+H2O2 solution at 37oC. This method provides a new model to mimic and directly detect DNA damage induced by chemical pollutants and their metabolites in vitro. The results indicated that, in the presence of H2O2, HRP was activated and catalyzed the transformation of AA to glycidamide, which could form DNA adducts and induce more serious damage of DNA than AA. In order to further verify these results, UV-vis spectrophotometry was also used to investigate DNA damage induced by AA and its metabolites in solution and the similar results were obtained.
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