Sensor Construction Based On Co₃O₄ Nanosheets And Its Application In The Detection Of Hydrogen Peroxide And Dopamine

Biomolecules play a very important role in human metabolism and life process,such as hydrogen peroxide（H₂O₂）and dopamine（DA）.Changes in their concentration can be regarded as signals of some diseases.Therefore,the development of accurate detection methods for biomolecules is of great significance for the diagnosis of diseases.In this thesis,cobalt trioxide（Co₃O₄）nanosheets were synthesized by hydrothermal and thermal decomposition two-step method,and silver loaded cobalt trioxide（Ag-Co₃O₄）nanosheets were synthesized by in-situ chemical reduction synthesis as the carrier.The two Co₃O₄ nanosheets were used to modify glassy carbon electrode to construct Co₃O₄ electrochemical sensor for H₂O₂ detection.At the same time,the Co₃O₄ nanosheet was used for the determination of DA by colorimetric method.The main research contents of this thesis are as follows:1.Synthesis of Co₃O₄ nanosheets and electrochemical sensor for H₂O₂detection and analysis.Co₃O₄ was synthesized by hydrothermal-thermal decomposition.Using cobalt chloride hexahydrate（Co Cl₂·6H₂O）and Octylamine as raw materials,the precursor cobalt hydroxide（Co（OH）₂）nanosheets were firstly prepared by hydrothermal method,and then the precursor was calcined at high temperature to synthesize the black powder Co₃O₄ nanosheets.Then,the Co₃O₄ nanosheet was drip-coated to the bare glassy carbon electrode to obtain the Co₃O₄electrochemical sensor and used to detect H₂O₂.Among them,the surface of Co₃O₄ nanosheet calcined at 200℃is distributed with many cracks,and the H₂O₂ electrochemical sensor modified by it shows the best electrochemical performance.When H₂O₂ concentration is in the range of（0.01-0.2 mmol/L）,the response current of the electrode shows a good linear relationship with H₂O₂ concentration.The detection limit is 6.53μmol/L（S/N=3）and the sensitivity is 875.66μA/（m M·cm²）,but the selectivity of the sensor for H₂O₂detection needs further improvement.2.Synthesis of Ag-Co₃O₄ nanosheets and electrochemical sensor for H₂O₂ detection and analysis.In order to improve the selectivity of the sensor for H₂O₂ detection,the Ag-Co₃O₄ nanosheet sensor was studied by using silver nanoparticles as another catalytic center.Ag-Co₃O₄ nanosheets were synthesized by in situ chemical reduction of Ag loaded on flake Co₃O₄ by calcination at 200℃as carrier,silver nitrate（Ag NO₃）as precursor and ascorbic acid（AA）as reducing agent at room temperature and water dispersion solution.The nanosheet was further coated on glassy carbon electrode by drop coating method to construct H₂O₂ electrochemical sensor.The results show that the response current of the electrode has a good linear relationship with H₂O₂ concentration in the range of 0.005-5 mmol/L,the detection limit is increased to 0.92μmol/L（S/N=3）,and the sensitivity is 764.70μA/（m M·cm²）.In the presence of ascorbic acid,glucose and uric acid,the pair sensor showed good selectivity for H₂O₂detection.3.Colorimetric detection and analysis of amines based on Co₃O₄nanosheet nanocrase.Finally,a simple colorimetric method for the detection of DA was established based on the oxidase activity of Co₃O₄ nanosheets.Co₃O₄nanosheets can catalyze the oxidation of colorless oxidase substrates（3,3,5,5-tetramethylbenzidine,TMB）to blue ox TMB in the presence of dissolved oxygen and no hydrogen peroxide,which has a characteristic absorption peak at 652 nm.The results showed that Co₃O₄ nanosheets calcined at 200℃had a stronger affinity with TMB and showed better catalytic activity.The enzyme dynamic Michler constant and maximum reaction rate were K_m=0.058mmol/L and V_max=1.27μmol/（L·S）,respectively.The presence of DA inhibited the TMB-O₂-Co₃O₄ reaction system,thus reducing its enzyme activity,and caused the color extinction and absorbance of the system weakened.Based on this,a colorimetric detection method for DA was established.The concentration range of DA was 1.6μmol/L-20μmol/L,and the reduction of absorbance showed a good linear relationship with the concentration of DA.The detection limit is 0.82μmol/L,and the colorimetric method has strong anti-interference ability for DA detection.