The New Electrochemical Analysis Method Study For The Determination Of Neurotransmitters

Neurotransmitters are the chemicals in the central nervous system that play importantroles in the signal transduction and information modification. The determination ofneurotransmitters and its concentration change can be used to the diagnosis of disease andquality control for the related drugs. Due to some outstanding advantages such as speediness,sensitivity, convenience, innocuity, low cost and portability, the electrochemical techniqueshave potential applications in environmental monitoring, clinical diagnosis, chemicalmeasurements and food industry. Carbon fiber microelectrode and the screen-printedelectrode are usually used as the based electrodes because of its small volume and portability.Carbon nanomaterials such as graphene, carbon nanotubes and ordered mesoporous carbonhave unique spatial structures and excellent properties, which make them suitable forapplications in optics, electricity, magnetism, biology, catalysis, sensors and energy storage.In this thesis, the sensors based on the graphene and graphene-Iron-tetrasulfophthalocyanine nanocomposite for the determination of neurotransmitters wereprepared and the electrochemical behaviors of the nanocomposite materials were studied.Additionally, a competitive electrochemical reaction between oxygen and drugs at the orderedmesoporous carbon is also investigated. The main works of this thesis are concisely describedas follows:（1） A novel graphene-modified carbon fiber microelectrode （GCFME） for the detectionof dopamine in mice hippocampus tissue was prepared. The electrochemical behavior ofGCFME is characterized by potassium ferricyanide, dopamine （DA）, ascorbic acid （AA） anduric acid （UA） by cyclic voltammetry （CV）. It was found that graphene makes a morefavorable electron transfer process for the oxidation of DA, AA and UA. The microsensor forDA has a linear range of4-order magnitude between1.0×10^-8M to1.0×10^-4M and anexcellent sensitivity with a detection limit of1.0×10^-8M and a good selectivity against AAand UA. The release of dopamine from hippocampus tissues of the mice brain at the miceconvulsion experiment model was successfully monitored by the GCFME. Thisgraphene-based voltammetric microelectrode offers a new way to monitor DA in mice braintissue in vivo.（2） Iron-tetrasulfophthalocyanine （FeTSPc） functionalized graphene composites weresuccessfully prepared based on the π-π interaction. The characteristics and electrochemicalsensing features of this composite for DA and serotonin （5-HT） was studied at theFeTSPc-GR modified carbon fiber microelectrode （GCFME）. The noncovalently FeTSPc-functionalized GR （GR-FeTSPc） possess an improved solubility in aqueous solutionand the GR-FeTSPc film electrode exhibits an enhanced electrocatalytic activity towardsoxidation of DA and5-HT. DPV was used to determinate DA and5-HT simultaneously. Themicrosensor for DA and5-HT has a good selectivity against AA and homovanillic acid. Theapplication of this microsensor was used to monitor the release of DA and5-HT at the micebrain on line in vivo and the concentration change of DA and5-HT in the mouse brain withtime was also investigated. The results are in accordance with that detected by highperformance liquid chromatography （HPLC）.（3） A comparative optical and electrochemical characteristic was studied betweenIron-tetrasulfophthalocyanine functionalized graphene composites （GR-FeTSPc） andIron-tetrasulfophthalocyanine functionalized multi-walled carbon nanotubes（MWCNTs-FeTSPc） composites. The energy gap of MWCNTs-FeTSPc between HOMO andLUMO is wider than that of GR-FeTSPc with UV and FTIR. On the screen-printed electrode（SPE）, DA、UA、AA and norepinephrine （NE） as the redox probes, CV results demonstratethat the strong electrocatalytic ability at both the GR-FeTSPc and the MWCNTs-FeTSPccomposites. Amperometric experiment indicates DA、UA、AA and NE have broad linearrange at the GR-FeTSPc modified SPE and the two kinds of electrodes show the sameprecision and selectivity. GR-FeTSPc and MWCNTs-FeTSPc composites have the similaroptical and electrochemical characteristic, but the GR-FeTSPc composites are more suitablefor electroanalysis.（4） A highly sensitive and selective electrochemical sensor for determination ofhydrogen peroxide （H₂O₂） by iron-tetrasulfophthalocyanine-graphene-Nafion（FeTSPc-GR-Nafion） modified screen-printed electrode was prepared. The nanocompositefilm （FeTSPc-GR-Nafion） exhibits an excellent electrocatalytic activity towards the oxidationof H₂O₂at a potential of+0.35V in the absence of enzyme. A comparative study usingdifferent graphene nanocomposite films reveals that the interactions between graphene andFeTSPc enhance the electrocatalytic ability and facilitate the electron transfer. Amperometricexperiment indicates that the sensors possess wide linear range from2.0×10^-7M to5.0×10^-3M with a detection limit of8.0×10^-8M （S/N=3）. The sensitivity of the H₂O₂sensor is36.93μA mM^-1cm^-2. In addition, the sensors show good selectivity for H₂O₂detection in thepresence of AA, DA, UA, glucose （Glu） and ethanol under physiological pH condition.Successfully, this sensor of such attractive analytical performances has been used to developthe glucose biosensor and also applied to determine H₂O₂in sterile water. The operating simplicity and low expense of fabrication make this sensor more attractive.（5） A selective and sensitive determination of oxygen on ordered mesoporous carbon（OMC） Nafion composite film modified glassy carbon electrode （GCE） was prepared. Theelectrocatalytical reduction of oxygen was at the potential of-0.47V in0.01M pH7.4phosphate buffer solutions （PBS）. A competitive electrochemical reaction between oxygenand chloramphenicol （CAP） on OMC/Nafion composite film-coated GCE was studied by CV.The results reveal that the reduction peak of oxygen moves positively to-0.35V, however thereduction peak of CAP moves negatively to-0.79V. Oxygen and CAP can be simultaneouslydetected with linear scan stripping voltammetry （LSSV）. In N2-saturated, air-saturated andO₂-saturated PBS （pH7.4）, the concentration of oxygen shows a good linear range with thecorrelation coefficient of0.999. The calibration curve was linear in the CAP concentrationrange of5.0×10^-7-6.0×10^-5mol L1with the detection limit of8.5×10-9mol L^-1（S/N=3）by linear scan stripping voltammetry （LSSV）. The electrode was successfully applied to thedirect determination of CAP and oxygen in honey samples.