| Chemically modified electrodes have been widely applied in analytical chemistry, and they play an important role in inorganic and organic compounds, biology, determination of active substances and analysis of valence, etc. Carbon ionic liquid electrode is one of the chemically modified electrodes, it is a new type of sensor, which is constructed by using ionic liquid as binder in place of non conductive organic binders.Electrochemical reaction usually occurs around the surface of the electrode. Due to the limitation of the electrode materials, how to improve the electrode surface property has become electrochemical workers’ new tasks. Through modifying carbon ionic liquid electrode, we can change the microstructure of the electrode surface. The obtained modified carbon ionic liquid electrode could separate and accumulate analytes effectively, and further enhance the selectivity, and could combine the sensitivity of determination methods with the selectivity of modifier. So chemically modified carbon ionic liquid electrode is a perfect system with separation, accumulation and selectivity. In this paper, we have studied a series of new electrochemical sensors which are based on various materials and different methods, and have discussed their applications in biological and environmental analysis. The main points of this dissertation are summarized as follows:(1) Due to its uniform pore structure, high surface areas and good biocompatibility, the mesoporous silica sieve MCM-41can provide a suitable matrix for immobilization of biomolecule. In this paper, the MCM-41was used to modify carbon ionic liquid electrode (CILE), and the hemoglobin (Hb) was immobined on the modified electrode by absorption, and a new biosensor was constructed. Hb kept its secondary structure similar to its native state in the modified electrode. The MCM-41modified CILE showed significant promotion to the direct electron transfer of Hb, which exhibited a pair of well defined and quasi-reversible peaks for heme Fe(Ⅲ)/Fe(Ⅱ) with a formal potential of-0.284V (vs. Ag/AgCl). Additionally, the Hb immobilized on the MCM-41modified carbon ionic liquid electrode showed excellent electrocatalytic activity toward H2O2. The electrocatalytic current values were linear with increasing concentration of H2O2in a wide range of5-310μM and the corresponding detection limit was calculated to be5×10-8M (S/N=3). The surface coverage of Hb immobilized on the MCM-41modified carbon ionic liquid electrode was about2.54×10-9mol cm-2. The Michaelis-Menten constant K1napp of214μM indicated that the Hb immobilized on the modified electrode showed high affinity to H2O2. The proposed electrode had high stability and good reproducibility due to the protection effect of MCM-41and ionic liquid, and it would have wide potential applications in direct electrochemistry, biosensors and biocatalysis.(2) A simple, sensitive, and reliable method based on a molecular sieve/ionic liquids composite electrode has been successfully developed for selective determination of dopamine (DA). In the composition molecular sieve HZSM-5with huge surface areas and ordered uniform pore structure can increase the efficient area of the modified electrodes and promote electron transfer. The HZSM-5can also act as a cation exchanger, and exhibit ion exchange or adsorption capabilities. Therefore, the molecular sieve/ionic liquids composite electrode shows increased response current for DA. At the optimum conditions, the peak current of DA was linear with the concentration of DA in the wide range of5.0×10-8mol L-1to8×10-4mol L-1, with the correlation coefficient of0.9982. The detection limit was1.0×10-8mol L-1(S/N=3) in the presence of0.2mM ascorbic acid (AA). The interference studies showed that the modified electrode had excellent selectivity. What’s more, the modified electrode also exhibited good reproducibility and stability for determination of DA, and could be applied to determine human serum samples.(3) A multi-walled carbon nanotubes (MWNTs) modified carbon ionic liquid electrode (CILE) had been successfully developed for determination of dopamine (DA) by dripping method. The acid-treated MWNTs with carboxylic acid functional groups could promote the electron-transfer reaction of DA. Due to the good performance of the ionic liquid, the electrochemical response of DA on the MWNTs/CILE was better than that of other MWNTs modified electrodes. In the presence of0.5mM ascorbic acid (AA), a linear calibration plot was obtained in the range5.0×10-8-2.0×10-4mol L-1and the detection limit was1.0×10-8mol L-1.(4) Electropolymerization is a good approach to immobilize polymers to construct polymer films modified electrodes. The polymer films prepared by electropolymerization are uniform and stable, and the thickness of the film can be controlled by number of growth cycles. The electrochemical polymerization of glycine on carbon ionic liquid electrode (CILE) was described in this paper. The presence of ionic liquid on the surface of CILE could facilitate the electropolymerization of glycine. The proposed sensor not only decreased the voltammetric responses of AA but also dramatically enhanced the oxidation peak current of DA compared with bare CILE. Using square wave voltammetry, the modified CILE showed good electrochemical behavior to DA in the physiological environment, the linear range of1.0×10-7-3.0×10-4M in the presence of1mM ascorbic acid (AA) and the detection limit of5.0×10-9M was estimated (S/N=3). (5) Nitrite plays an important role in industry and daily life, but its potential toxicity is not been ignored. So a simple and reliable method for the determination of nitrite was described based on a titanium dioxide modified carbon ionic liquid electrode. The modifier titanium dioxide could improve the properties of the electrode and the surface area of the sensor was enhanced evidently. So the proposed sensor showed electrocatalytic activity for the oxidation of nitrite and the oxidation peak occurred at low overpotential (0.78V versus Ag/AgCl). The catalytic peak current was found to be linear with the nitrite concentration in the range of5×10-7-1.5×10-3M, with a correlation coefficient of0.9977, using linear sweep voltammetry. When the S/N=3, the detection limit of2×10-7M was obtained. The sensor had good reproducibility and stability. Possible interferences from several common ions were evaluated, and the result indicated the sensor showed excellent selectivity for nitrite. This sensor was applied for the voltammetric determination of nitrite in some sausage samples, and the satisfactory results were obtained.(6) Uric acid (UA) is a primary end product of purine metabolism and it usually coexists with ascorbic acid (AA) in human liquid, such as serum and urine. Abnormal levels of UA are symptoms of several diseases like gout, hyperuricaemia and Lesch-Nyhan syndrome. So in this paper a chitosan/ionic liquid composite electrode was prepared and used to determine uric acid in the presence of a large excess of A A and dopamine (DA). The modified electrode showed large peak separations between DA, AA and UA. Due to the existence of chitosan and ionic liquid in the composition, the modified electrode displayed strong electrochemical catalytic activity toward the oxidation of UA. Under the optimal conditions, the peak current was linearly dependent on the UA concentration in the range of5×10-7M-2×10-4M in the presence of5×10-4M AA and5×10-5M DA with a correlation coefficient of0.9978, and the detection limit was5×10-8M at a signal-to-noise ratio of3. With good sensitivity, selectivity and stability, the present modified electrode has the potential for the determination of UA in the practical application. |
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