Preparation And Electrochemical Properties Of Grapheme Composite Nanoparticles For Dopamine Sensing Determination

Dopamine（DA）is an important catecholamines neurotransmitter which plays an important role in the prevention and control of diseases in the central nervous systerm.Therefore,the determination of DA has a great significance in clinical application and the physiological mechanism analysis.Electrochemical method has drawn a wide attention among many researchers due to its simplicity and low cost.Graphene as a promising material,has many unique physical and chemical properties,such as large specific surface area,good electrical conductivity,and excellent mechanical strength,which plays an important role in the preparation of novel electrode materials with high sensitivity and high selectivity.With the development of composite materials,a variety of electrode modifier such as conduct polymer film,metal nanoparticles and carbon nanoparticles have been reported to determinate DA.Especially,the nanoparticles and semiconductor material have remarkable performance in DA detection.In this paper,graphene-metal oxide nanohybrid were prepared for the determination of DA.It is well known that there are two coexistence biological substances of ascorbic acid（AA）and uric acid（UA）,which were usually coexist with DA in the extracellular fluids.The oxidation peaks of DA,AA and UA at potentials are very close to each other,resulting in an overlapping voltammetric response.Thus,it is necessary to develop sensitive and selective methods for simultaneous determination of the species for both analytical applications and diagnostic research.In this thesis,several electrochemical sensors based on graphene-metal oxide hybrid were fabricated and their application in electrochemical sensors for the selective determination of DA were investigated in detail.The main contents of this thesis are as following:1.The grapheme/Fe₃O₄ nanoparticles composite was prepared to modify glassy carbon electrode for the determination of DA.The morphology of the amino-group functionalized Fe₃O₄ was investigated by SEM and TEM.As can be seen,the prepared Fe₃O₄ was mesoporous structure with diameter about 50 nm.The amino-group functionalized Fe₃O₄ was mixed with graphene oxide（GO）at certain mass ratio and stirred vigorously for 2 h.Then,a certain amount of GO-Fe₃O₄ dispersion was dropped on the freshly prepared GCE surface and electrochemically reduced to obtain graphene-Fe₃O₄ modified glassy carbon electrodes（ERGO-Fe₃O₄/GCE）.The peak current of DA on the ERGO-Fe₃O₄/GCE was twice larger than thaton the ERGO/GCE.The experimental conditions are optimized.According to experimental results,the reducing potential was chosen as-1.5 V,the reducing time as120 s,the accumulation potential as 0 V,the accumulation time as 180 s,and the solution pH 3.5.There is a good linear relationship between the peak current and scan rate within the investigated range,which indicates that the oxidation of DA follows a adsorption controlled electron transfer process.The modified electrode has good anti-jamming capability,which can be used for the simultaneous determination of DA,AA and UA.The peak current of DA increases linearly with DA concentration in the range of 6×10^-9 mol/L⁸×10-5 mol/L,with a detection limit of 4.0×10^-9 mol/L.2.In this part,Cu₂O nanoparticles-graphene composite was fabricated and modified on the surface of glassy carbon electrode to detect dopamine.The Cu₂O nanoparticles was fabricated by reducing CuSO4·5H2O with hydrazine hydrate.The prepared Cu₂O was well-defined nanocubes from SEM images.The current of DA on the Cu₂O-graphene modified electrode was better than that on the graphene modified electrode.According to the optimum conditions,the reducing potential was chosen as-1.5 V,the reducing time as 300 s,the accumulation potential as-0.1 V,the accumultion time as 150 s,and the solution pH as 3.5.There is a good linear relationship between the peak current and scan rate within the investigated range,which indicates that the oxidation of DA follows a adsorption-controlled electron transfer process.The modified electrode can be used for the simultaneous determination of DA,AA and UA,showing a good anti-jamming capability.The peak current of DA increases linearly with DA concentration from 1.0×10^-8 mol/ L to8.0×10-5mol /L,with a detection limit of 6×10^-8mol/L.3.Hereby,manganese dioxide（MnO₂）with three different morphologies including nanorods,nanotubes,and nanowires were prepared by facile hydrothermal synthesis and then loaded on graphene to fabricate MnO₂-reduced graphene oxide nanocomposites,which was applied to prepare DA electrochemical sensors.It was found the largest current of DA was obtained on the MnO₂ nanowires-graphene composite film modified electrode.According to the optimum conditions,the reducing potential was chosen as-1.5 V,the reducing time as 120 s,the accumulation potential as-0.1 V,the accumultion time as 120 s,and the solution pH as 3.0.There is a good linear relationship between the peak current and scan rate within the investigated range,which indicates that the the electrode reaction of DA was adsorption-controlled process.The modified electrode was used for the simultaneousdetermination of DA,AA and UA molecules and have better anti-jamming capability.The peak current increased linearly with increment of DA concentration in the range of 1×10^-8 mol/L⁸×10-5 mol/L,with a detection limit of 1×10^-9mol/L.