【作者】 李永红；

【导师】 魏万之； 蔡青云；

【作者基本信息】 湖南大学 ， 分析化学， 2012， 博士

【摘要】 化学修饰电极在分析化学中有着很广阔的应用前景,在无机物、有机物和生物以及其活性物质的测定、价态分析等诸多方面都发挥着很大的作用。碳离子液体电极是化学修饰电极中的一种,它是利用导电的离子液体代替传统的非导电的石蜡油等作为粘合剂而制备的一类新型电极。电化学反应一般是在电极表面附近进行的,由于电极材料种类的限制,如何改善现有电极的表面性能,给电极赋予所期望的特性,已经成为电化学工作者研究的新课题。通过对碳离子液体电极进行修饰,可以改变电极表面的微结构。得到的化学修饰碳离子液体能对待测物进行有效地分离富集,进一步提高选择性,而且还能把测定方法的灵敏性和修饰剂化学反应的选择性相结合,因此化学修饰碳离子液体电极是集分离、富集和选择性三者为一体的理想体系。本论文利用各种的修饰材料和不同的修饰方法构建了一系列新型的电化学传感器,并结合使用不同的测定方法讨论了其在生命和环境分析中的应用。主要研究工作如下：(1)由于介孔分子筛MCM-41具有均一的孔道结构、较大的比表面积和很好的生物适配性等优点,它能为生物分子的固定提供了一个良好的微环境,因此我们将MCM-41修饰到碳离子液体电极表面,然后通过吸附的方法将血红蛋白(Hb)固定到修饰电极上,构建了一种新型的电化学生物传感器。固定在该修饰电极上的血红蛋白能很好地保持其二级结构,在该修饰碳离子液体电极上能够实现血红蛋白的直接电化学。在-0.284V左右能观察到血红蛋白的一对可逆的峰形很好的氧化还原峰。此外,该生物传感器对H202表现出良好的电催化活性,催化电流与H202的浓度在5-310μM内呈良好的线性关系,在信噪比为3的前提下检测限达到了0.05μM。血红蛋白在MCM-41修饰的碳离子液体电极上的表面覆盖率为2.54×10-9mol cm-2,米氏常数为214μM,说明固定在修饰电极上的血红蛋白对H202显示了很好的亲和性。由于MCM-41和离子液体的共同作用,提出的传感器具有很好的稳定性和重现性,能应用于直接电化学、生物传感器和生物催化等方面的研究。(2)成功构建了分子筛/离子液体复合物电极,提出了一种选择性检测多巴胺(DA)的简单、灵敏、可靠的方法。复合物中具有较大比表面积、均一孔道结构的分子筛HZSM-5能够增加修饰电极的有效面积,并促进修饰电极的电子转移能力。HZSM-5也同时扮演着阳离子交换剂的角色,表现出离子交换或吸附能力,因此,该修饰电极显示了对多巴胺选择性的增强的电化学响应。在最优的实验条件下,DA对应的峰电流与浓度在5.0×10-8到8.0×104M的范围内成线性关系,且线性相关系数为0.9982。在0.2mM抗坏血酸(AA)存在下,检测限达到了1.0×10-8M。干扰研究表明,该修饰电极具备很好的选择性。而且,该修饰电极具有很好的重现性和稳定性,能用于实际样品人体血清中多巴胺的检测。(3)通过滴涂的方法,将活化的多壁碳纳米管(MWNTs)修饰到碳离子液体电极表面,构建了多巴胺传感器。在生理条件下,由于活化的多壁碳纳米管带有羧基官能团,该修饰电极对多巴胺表现出增强的电化学响应。和其它多壁碳纳米管修饰电极相比,多巴胺在多壁碳纳米管修饰的碳离子液体电极上的电化学响应显著增加,这是由于碳离子液体电极中具有良好性能的离子液体的促进结果。在0.5mM抗坏血酸(AA)存在下,响应电流与DA的浓度在5.0×10-8至2.0×104M的范围呈线性关系,最低检测限达到了1.0×10-8M。此外,该传感器还能用于实际样品的检测。(4)电化学聚合是一种固定聚合物的很好的方法,电化学聚合得到的聚合物膜具有均一稳定的性质,膜厚度可以通过扫描圈数来控制。我们通过电化学聚合的方法,将甘氨酸聚合到碳离子液体电极表面。研究表明,碳离子液体电极中离子液体的存在能够促进甘氨酸的电聚合。和裸碳离子液体电极比较,该修饰电极不仅能够抑制抗坏血酸(AA)的伏安响应,而且能够显著增加多巴胺(DA)的氧化电流。在生理环境中利用方波伏安法(SWV),该聚甘氨酸修饰电极对DA显示了很好的电化学行为。在1mM AA存在下,DA的响应电流与浓度在1.0×10-7至3.0×10-4M的范围呈线性关系,检测限达到了5.0×10-9M。(5)亚硝酸盐在工业生产以及人们的日常生活中发挥着很重要的作用,然而它潜在的毒性也不容忽视,因此我们介绍了一种基于纳米二氧化钛修饰碳离子液体电极的检测亚硝酸盐的简单可靠的方法。修饰剂二氧化钛改善了修饰电极的微结构,使修饰电极的有效表面积显著增加,因此,该传感器对亚硝酸盐的氧化体现了很好的电催化活性,且氧化峰电位出现在较低的电位(约0.78V versus Ag/AgCl)。在最优的实验条件下,利用线性扫描伏安法对亚硝酸盐进行检测,其峰电流与亚硝酸盐的浓度在5×10-7M至1.5×10-3M的范围内成线性关系,线性相关系数为0.9977。当信噪比为3时,检测限达2×10-7M。该传感器具有很好的重现性和稳定性。干扰实验结果表明,常见离子不会影响亚硝酸盐的检测,该传感器对亚硝酸盐的检测具有很好的选择性。该传感器还可以应用于几种香肠样品中亚硝酸盐的伏安检测,并获得满意的结果。(6)尿酸(UA)是一种嘌呤代谢的终产物,通常和抗坏血酸(AA)共存于人类流体中,如血液和尿液等。当尿酸含量发生异常时,通常会引发其他疾病,如痛风、高尿酸血Lesch-Nyhan综合征等。基于此,我们构建了一种新型的壳聚糖/离子液体复合物电极,能在大量抗坏血酸和多巴胺存在下选择性检测尿酸。多巴胺、抗坏血酸和尿酸的氧化峰在修饰电极上能够很好地分离开来。由于复合物中壳聚糖和离子液体的共同作用,该修饰电极对尿酸的氧化显示了很好的电催化活性。当5×10-4M抗坏血酸和5×10-5M多巴胺共同存在时,响应电流与尿酸的浓度在5×10-7M到2×104M的范围内成线性关系,线性相关系数为0.9978。在信噪比为3的条件下,检测限达到了5×10-8M。该修饰电极具有很好的灵敏度、选择性以及稳定性,因此该修饰电极具有用于实际样品中尿酸检测的潜力。更多还原

【Abstract】 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.更多还原