Study Of Electrochemical Sensor Based On Novel Nanomaterial Modified Electrodes

Due to their high sensitivity , excellent selectivity, low cost, rapid reponse and continuous detection in perplexing system, electrochemical biosensor has comprehensive valuable applications in bioengineering, clinical medicine, environmental protection, electonic and food-stuff industry. Because of a number of advantages, nanostructured materials are fitted for the preparation of sensor, and enhance their response performance. Magnetic Fe₃O₄ nanoparticles（Fe₃O₄-NPs） possess unique magnetic action, eminent electronic conduction , excellent biocompatibility and catalytic property, they have attracted considerable attentions in many fields, including material production, mimetic catalysis, biomedicine, and so on. Nature enzymes own high catalytic efficiency and perfect selectivity for substrate, however, they are relatively difficult to be extracted and critical to the environmental condition. Furthermore, the enzymes cannot keep a long-term stability due to their inherent instability, so the assembly-line production of nature enzymes may suffer from lots of difficulties. Thereore , it may make sense for exploiting functional materials. In this study, we succeeded to fabricate an electrochemical sensor based on novel nanomaterials, and used for the detection of hydrogen peroxide. Electrochemical DNA biosensor integrates electrochemistry with molecular biology, which makes far-reaching influence for clinical medicine and genetic engineering, as a result, a great number of attentions are awared by scholars recently. According to the above discusses, an original electrochemical DNA sensor was prepared to detect dopamine without interference. At the same time, the sensor paves a new way to the study of electrone transfer and metabolism in life. The details are described as follows:（1） Fe₃O₄-NPs were synthesized by co-precipitation method. After preparation , the self-synthesized nanoparticles were empolyed as a part of sensor and used for constructing modified electrode. We adopted physical adsorption method to manufacture electrode. The procedures are illuminated in the following essay. First of all, Fe₃O₄-NPs were dispersed in PDDA solution, then we added several drops to the carbon electrode. After the liquid drops dried in the air, another kind of drop called Nafion was added onto the carbon electrode , successively, which could prevent from the sensitive materials letting out. Fe₃O₄-NPs possess mimetic catalysis to hydrogen peroxide. In this experiment, the electrochemical sensor represented great response behavior to hydrogen peroxide with a linear rangeof 10μM～2 mM, and the related coefficient was 0.9929. According to Michealis equation based on the analysis of different concentration of hydrogen peroxidase, the related coefficient was 0.9989 and the Michaelis constant was 5.1 mmol/L,respectively,indicting that the self-preparation sensor displayed excellent catalysis capabililties to hydrogen peroxidase.（2） We fabricated CNTs and Fe₃O₄-NPs mixed electrode by chemical and static adsorption method. The functionalized electrode capabilities were investigated by cyclic voltammograms（CVs） and amperometric i-t curve, such as direct CVs, electrocatalytic CVs and advantages of the carbon nanotubes. The sensor could be used for the detection of hydrogen peroxide, and the linear range was 5μM～2.5 mM . Because the force between chemical and static adsorption were greater than simple physical adsorption, so this modified electrode represented properties in stability and repeatbalility.（3） DNA modified electrode was constructed by electrodeposition. The carbon electrode surface was overlayed by DNA after electrodeposition. In the rear of DNA, there exited much phosphate anion with negative charge, which could arrest dopamine, for dopamine moleculars were positive. This process could evidently amplify the anodic current. More importantly, the modified electrode successfully separated the anodic peaks between dopamine and asorbic acid , compared to normal bare electrode. We used impulse voltammograms to detect dopamine selectively and sensitively. The concentration of dopamine was allowed to 0.05μM could be detected, and the low limit is 0.05μM. Considering the preparation of electrodeposition DNA modified electrode was convient and efficient detection for dopamine, it may provide a broad platform for the detection of dopamine.