| Electrochemical sensors are centered great expectations for their obvious advantages, such as portability, low-cost, sensitivity and stability. Among them, electrochemical biosensors, which employ electrode as transducer and biomaterials as sensing organ, are ideal devices for directly and selectively getting information from a complex system by monitoring the signal of potential, conductance or current. It is an attractive strategy to develop novel biosensors via the modification of electrode and biomolecules. Especially, the nanostructure materials can be exploited to increase the conversion of information between the target substance and electrode in the investigation of bioelectrochemistry and related fields. So far there are still great opportunities for us to carry on further research.Carbon nanotubes (CNTs) exhibit many extraordinarily attractive physical and chemical properties, such as the large surface area, the good ability to promote electro-transfer reactions, remarkable catalysis towards biomolecules, good biocompatibility, accumulating many kinds of molecules and etc. Room temperature ionic liquids (RTILs) can be used as electrolyte as well as solvent. They also have attracted considerable attention due to their unique physical and chemical properties, such as high thermal and chemical stability, high conductivity, the ability to dissolve a wide range of organic and inorganic molecules, wide electrochemical potential window, ability to facilitate direct electron-transfer reactions, good biocompatibility and etc. Since the introduction, CNTs and RTILs have received enormous attention in the fields of electrochemistry and analytical electrochemistry. Moreover, it's attractive that the combined application of them has more promising prospects in many fields of electroanalytical chemistry, for example, the fabrication of electrochemical sensors and electrochemical biosensors.The goal of the research work is the achievement of sensitive and practical electrochemical sensors and electrochemical biosensors. To fulfill it, CNTs are used to modify electrodes or to be assembled as array electrode to increase the electroanalytical properties of common electrode. Based on the preparation of the sensitive transducer, a sandwich-type mode, which is competent for trace amount detection, is established by employing RTILs as membrane material.The paper consists of ten chapters in all.The first chapter is the introduction of the subject. The background of the research is reviewed and the direction of my work is stated.DNA is the carriers of hereditary information and the basic substance of gene expression, and plays key roles in the growth, development and breeding of lives. So, it's an important aspect to discover the information about DNA molecule. Electrochemical protocols exhibit many advantages in the assay of DNA, such as high sensitivity, low detection limit, low cost, fast response, and so on. From Chapter Two to Chapter Six, the contents are focused on the investigation of DNA and related molecules at the sensitive modified electrode. Combining polymerase chain reaction (PCR) technology or using label-free hybridization biosensor, we established two modes to detect sequence-specific DNA related to genetically modified organisms (GMOs) successfully with voltammetric methods.In Chapter Two, the treated multi-walled carbon nanotubes (MWNTs) are coated onto the glassy carbon electrode (GCE) to fabricate a modified electrode (MWNT/GCE). At the MWNT/GCE the electrochemical behaviors of 2′-dexyguanosine 5′-triphosphate trisodiums salt (dGTP), which is one of the four reactants in PCR, are investigated. In 0.2 mol/L B-R buffer solution the oxidative peak potential (Epa) of dGTP at the MWNT/GCE shifted 0.108 V negatively in contrast to that at the GCE. And the oxidative peak current (ipa) increased dramatically in contrast to that at the GCE. The electron-transfer coefficientαand the heterogeneous electron transfer rate constant k's are 0.50 and 0.16 s-1, respectively. Chapter Three centers the establishment and application of a fast and cost-effective protocol for detecting sequence-specific DNA by combining PCR and electrochemical technologies. Characterizing with cyclic voltammetry by using potassium ferricyanide and methylene blue (MB) as probes, we find that the short single-walled carbon nanotubes (S-SWNTs) modified glassy carbon electrode (S-SWNT/GCE) has attractive electroanalytical properties. A dramatic enhancement of the ipa and a visible decrease of overpotential towards dGTP can be realized at it. The ipa of the free dGTP decreases remarkably after a successful PCR amplification owing to the participation of the free dGTP as one of reactive substances for the PCR products, namely dsDNA. Based upon this response change of the free dGTP before and after incorporation in PCR, the target gene in the DNA template is present or not can be deduced. Thus, the GMOs sample, which provides template DNA, can be detected easily. And the result is in good accordance with that obtained with gel electrophoresis.In Chapter Four, a gel-like paste is made by mixing 1:1(w/w) S-SWNTs and a kind of RTIL of 1-butyl-3-methylimidazolium hexafluorophosphate (BMIMPF6). The composite film is modified onto the GCE to prepare the S-SWNT&RTIL/GCE. The modified electrode shows attractive electrocatalytic ability and can enhance the current response of electro-active molecules by employing potassium ferricyanide, AA and MB as probes. ssDNA has a sensitive voltammetric response at the S-SWNT&RTIL/GCE and the Epas of guanine base and adenine base are 0.532 V and 0.808 V, respectively. The heterogeneous electron transfer rate constants k's for the two bases are 1.84×10-2 s-1 and 3.69×10-2 s-1, respectively.The content of Chapter Five consists of the preparation, characterization and application of a novel kind of paste electrode (S-SWNT&RTIL PE), which is fabricated with S-SWNTs mixed RTIL of BMIMPF6. Its electrochemical behavior is investigated by voltammetry and electrochemical impedance spectroscopy (EIS) in comparison with the paste electrode using mineral oil as a binder. Results highlight the advantages of it: not only higher conductivity, but also lower potential separation (?Ep), higher peak current (ip) and better reversibility towards a number of molecules. Based on the current response of guanine bases, the S-SWNT&RTIL PE can be used to detect ssDNA sensitively with a detection limit of 9.9 pmol/L. And the number of guanine bases and adenine bases contents in per mol oligonucleotides can be monitored according to the current response within a rather wide range. In Chapter Six, carboxylic group-functionalized S-SWNTs are assembled vertically on the GCE using ethylenediamine as linking agent to fabricate an aligned electrode (SWNTE) in the presence of EDC and NHS. ssDNA wrap around the SWNTs to form ssDNA-wrapped-SWNTE structures based on the interaction between ssDNA and SWNT. Sensitive differential pulse voltammetric (DPV) responses are obtained at the ssDNA-wrapped-SWNTE owing to the electrooxidation of guanine bases and adenine bases. dsDNA is formed when ssDNA on the ssDNA-wrapped-SWNTE is hybridized with complementary ssDNA (cDNA). The dsDNA is removed from the SWNTs through preconditioning and rinsing processes. Consequentially, the DPV current response of guanine bases decreased. Based on this mechanism, a label-free and readily reusable electrochemical DNA hybridization biosensor is designed by directly monitoring the current change of guanine bases. The used SWNTE can be renewed easily via ultrasonically rinsing. Thus, the biosensor can be switched to detect different target DNAs easily.From Chapter Seven to Chapter Ten, the contents consist of the establishment of sandwich mode for trace amount detection and the application of the sensitive electrode in some other important molecules.In consideration with the advantages of SWNTs and RTIL in detecting target molecules (TMs), a novel strategy of sandwich-type electrode is established with TMs confined by RTIL between the S-SWNT/GCE and RTIL membrane. This strategy shows high sensitivity, good precision and good stability. It is of especial importance towards trace amount detection. It can be used for electrochemical detection of AA and dopamine (DA) with the detection limits of 400 fmol and 80 fmol, respectively. The selective detection of DA in the presence of high amount of AA can be performed, too.In Chapter Eight, the electrochemical properties of guanine at the S-SWCNT/GCE are studied. The Epa of guanine responds sensitively to the pH of buffer solution. Based on this, the S-SWCNT/GCE/guanine system is used to prepare a novel potentiometric pH sensor. The sensor shows linear response to pH values in the range of 2.0 - 12.0 with a slope of 0.0497 V/pH. And there is a remarkable potential jump on the potentiometric titration curve.In B-R buffer solution, the voltammetric responses of fullerene C60 and fullerene C60 nanotubes (FNTs) are investigated with sandwich mode at room temperature. The mechanism of the electrode processes are presumed for the first time. Moreover, with the aid of DNA, FNTs are dispersed into aqueous solution, followed by being immobilized onto the GCE surface. And the mechanism of the electrode process of FNTs is characterized further. After undergoing a reductive reaction in NaOH solution, the modified electrode can be used to selectively detect DA in the coexistence of AA owing to the perfect separation of their electrooxidative peaks.In the last Chapter, the catalytic electrooxidation of AA at the MWNT/GCE is investigated. AA has two well-separated oxiditive peaks in B-R buffer solution of pH 4.0 and the reaction mechanism is illustrated according to the molecular structure of AA and the carboxylic acid group-functionalized MWNTs. A rather low detection limit of AA is obtained with DPV measurement using MWNT/GCE as working electrode.
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