Development Of Chemical/Biosensors And Its Investigations And Applications In Chemical Analysis

Environmental science, life science and materials science are dominating the 21st century; all the basic studies and high-tech development in the scientific area need the support of the analytical science, which brought forward new challenges to it. Based on the chemically modified electrodes as chemo/biosensors, electrochemical voltammetry has several advantages in that the instrument is simple and suitable for constructing inexpensive and portable detectors, which aroses the research workers' attentions. In this thesis, a series of studies on the development of novel modified electodes as chemo/biosensors and their application in the analysis in environmental and biological area, and some valuble results were obtained. The main points of this thesis are summarized as follows:1. A novel sensor was fabricated by using a DNA-Ni2+/MWNTs/Chitosan complex membrane and the synergistic electrocatalytic effect of the complex membrane for the electro-oxidation of methanol was observed. The membrane composed of DNA, MWNTs and chitosan functioned as a support matrix for immobilization of electrocatalytic element-Nickel cation. The good electrocatalytic activity of the resulting DNA-Ni(Ⅱ)/MWNTs/chitosan/GC electrode was found by the electro-oxidation of methanol in alkaline medium. A linear range from 0.2 mmol·L-1 to 5.0 mmol·L-1 for the detection of methanol in alkaline medium was observed with a rapid response (within 3 s) and a detection limit of 10μmol·L-1 based on a signal-to-noise ratio of 3. In addition, the sensor exhibited good stability.2. A sensor for methanol was fabricated by incorporating the antibiotic cefixime (CEF) along with Ni2+ ion into a chitosan membrane matrix. Sensing is based on the electrocatalytic effect that the complex membrane exerts on the electro-oxidation of methanol. The resulting CEF-Ni2+/Chitosan glassy carbon (GC) electrode had a good electrocatalytic activity to the electro-oxidation of methanol in alkaline medium. Especially, the modified electrode had an immense electrocatalytic activity to the second process of methanol oxidation (methanol oxidation intermediate(s) to the final product). The modified electrode had a wide linear range from 20μmol·L-1 to 12 m mol·L-1 for the detection of methanol in alkaline medium and a low detection limit of 5.24μmol·L-1 based on a signal-to-noise ratio of 3. In addition, the sensor exhibited good stability.3. A DNA-Ni2+ complex film was modified onto the surface of glassy carbon (GC) electrode by using direct electrodeposited method. The role of DNA membrane was studied in detail. The nickel ions immobilized in the DNA membrane exhibited an excellent and stable catalytic activity to the electro-oxidation of methanol in alkaline medium. It was indicated that the DNA membrane would not block the methanol molecules diffuse into the catalytic active site in this modified membrane. Furthermore, it could make oxidation intermediate products which may poison the active site react sufficiently and diffuse out of the catalyst layer much easier. As a result, the DNA membrane was an ideal carrier for the Ni ion immobilizing, and the utilization efficiency of catalysts Ni2+ could get higher. A wide linear range from 8.0μmol·L-1 to 2.4 mmol·L-1 for the detection in alkaline medium and a low limit of 2.0μmol·L-1 based on a signal-to-noise ratio of 3 were presented. At last, it was noted that this sensor have merit stability and reproducibility. It was supposed a homologous membrane could be used to fabricate a metal anode with high catalytic activity, which would not easily be poisoned by methanol oxidation intermediate products, in the application of alkaline direct methanol fuel cells.4. A new composite film comprising cationic gemini surfactant butane-a,co-bis(dimethyl dodeculammonium bromide) (BDDA, C12-C4-C12) and poly (allylamine) hydrochloride(PAH) have been prepared. The composite film showed good biocompatibility and could promote the direct electron transfer between hemoglobin (Hb) and glassy carbon (GC) electrode. The immobilized Hb exhibited a pair of well-defined, quasi-reversible and stable redox peaks with a formal potential of -0.158 V (vs SCE) in 0.10 mol·L-1 pH 7 phosphate buffer solutions, and showed high affinity to hydrogen peroxide. The cathodic peak current of the electrode was linear with increasing concentration of H2O2 in the range of 5.14 to 200μmol·L-1.5. Simultaneous determination of dihydroxybenzene isomers was investigated at a MCNTs/(3-cyclodextrin composite modified carbon ionic liquid electrode in phosphate buffer solution (pH= 7.0) in the presence of cationic surfactant cetylpyridinium bromide (CPB). With the great enhancement of surfactant CPB, the voltammetric responses of dihydroxybenzene isomers were more sensitive and selective. The oxidation peak potential of hydroquinone was about 0.024 V, catechol was about 0.140 V and resorcinol 0.520 V in differential pulse voltammetric (DPV) measurements, which indicated that the dihydroxybenzene isomers could be separated entirely. The electrode showed wide linear behaviors in the range of 1.2×10-7-2.2×10-3,7.0×10-7-1.0×10-3,2.6×10-6-9×10-4mol·L-1 for hydroquinone, catechol and resorcinol, respectively. And the detection limits of the three dihydroxybenzene isomers were 4×10-8,8.0×10-8,9×10-7 mol·L-1, respectively.6. A series piezoelectric quartz crystal (SPQC) sensing technique was used to monitor unfolding and refolding processes of lysozyme by monitoring the change of conductivity in solution. The lysozyme was unfolded by sodium dodecylbenzene sulfonate (SDBS) and then refolded by cetyltrimethylammonium bromide (CTAB). During the unfolding and refolding process, the conductivity of the solution changed accordingly. A sensitive response caused by the change of solution conductivity could be monitored by SPQC sensor. The results indicated that the SPQC sensing technique could be used as a convenient tool for monitoring the interaction between ionic surfactants and protein.