| The existence of metal ions is essential but sometimes may be harmful for living organisms. The investigation on the influence of metal ions to DNA is of great significance. The heavy metal ions-nucleobases interaction is an important research topic in environmental and biochemical analysis. On the other hand, carbon nanotubes (CNTs), found in1991, with its special mechanical, electrical, optical, thermotical, magnetical and chemical properties have widely prospect on material science, physics and chemistry and so on. It is regarded as one of the most promising nano materials. Electrochemical biosensors based on CNTs modified electrodes has became one of the research hot topics. Furthermore, the characters of CNTs can be improved by doping with foreign atoms. And doping CNTs with B atoms can produce more edge sites on the surface of CNTs and oxygen-rich groups on the defect sites of CNTs. Then the electrocatalytic ability of CNTs can be improved due to the more reactive sites on its surface. Based on all above mentioned, the main points of this thesis are listed as follow:(1) A new electrochemical analytical method for indirectly detecting (Ag+) based on the interaction of Ag+and islolated guanine (G) was constructed. The presence of the Ag+may influence the formation of oxidation intermediate and the electrocatalytic oxidation activity of G, since Ag+can interact with G at the binding site N7which is involved in the electrocatalytic oxidation reaction of G. In order to improve the sensitivity of this sensor, CNTs was used to modify the glassy carbon electrode. This constructed sensor has many special characters including a broad liner range (100nM～2.5μM), low detection limit (30nM, S/N=3), high selectivity, good stability, simplicity, low cost and no requirement for probe preparation. In addition, this method has been successfully applied for the detection of practical water samples.(2) Based on the Ag+-G electrochemical sensor constructed above, the sensitive detection of cysteine (Cys) has been achieved. Cys can competitively with G to combine with Ag+because Ag+is apt to interact with the thiol group (-SH) of cysteine. The sensitive determination of Cys was achieves through the changes on the electrocatalytic oxidation signals of guanine. This method avoided the disadvantages produced by the high oxidation potential of cysteine itself. And the detection limit of this sensor was12nM (S/N=3). In addition, this method has some other characters, such as short detecting time and excellent selectivity.(3) Based on the complex of chitoson (CS) and Boron-doped carbon nanotubes (BCNTs) modified glassy carbon electrode (CS-BCNTs/GC), a new electrochemical sensor for nitrite ion (NO2) was fabricated. BCNTs can effectively promote the electron transfer between the NO2-and the electrode, and at the same time, the amine group (-NH2) of CS, which can transform to NH3+in acidic condition, was favorable for the absorption of NO2-. Compared to bare、CS modified and CS-CNTs modififed electrodes, CS-BCNTs/GC has better electrocatalytic ability. Comparing to other traditional electrodes modified by CNTs, the modified electrode we fabricated has broad response range (0.4μM～1mM), low detection limit (0.2μM, S/N=3) and good selectivity. |
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