Applications Of Electrochemical Sensors Based On Magnetic Nanoparticles In Detection For Hydrogen Peroxide Or Nitrite

Environmental and food safety is closely related to people’s health. With the rapid development of economy, people’s living standards are improving unceasingly. However, environmental pollution and illegal use of food additives have became a serious problem to harm people’s health. To effectively protect the environment and ensure food security, development of sensitive and accurate analytical techniques is of important significance.Hydrogen peroxide and nitrite, widely exist in industrial products, food, environment and so on, are important research objects in the environmental monitoring and food analysis. Fe3O4 magnetic nanoparticles are one of the most widely studied nanomaterials due to their advantages, such as easy preparation, low cost, low toxicity, intrinsic peroxidase-like catalytic activity, high electrical conductivity, appealing magnetic properties and so on. In this thesis, a summary on electrochemical sensors based on magnetic nanoparticle and its composites for the application on hydrogen peroxide and nitrite determination was introduced. A series of electrochemical sensors were prepared and their analytical performances on hydrogen peroxide or nitrite were discussed. Experimental results indicated that the constructed sensors were successfully applied to hydrogen peroxide or nitrite detection with good performance.Specific works were as follows:1. Determination of Hydrogen Peroxide Using a Novel Sensor Based on Fe3O4 Magnetic NanoparticlesFe3O4 magnetic nanoparticles (Fe3O4 MNPs) were synthesized by chemical co-precipitation with sodium citrate as a surfactant and were characterized by X-ray diffraction and atomic force microscope. Then the Fe3O4 MNPs and chitosan were used to construct a novel hydrogen peroxide sensor. Cyclic voltammetry curves indicated CS/Fe3O4/GC electrode electrocatalyzed the reduction of hydrogen peroxide. This novel nonenzyme sensor provided good sensitivity and stability, and precision with potential applications.2. A Novel Hydrogen Peroxide Biosensor Based on Fe3O4 Magnetic Nanoparticles and Horseradish Peroxidase with Graphene-Chitosan CompositeA novel hydrogen peroxide (H2O2) biosensor was constructed based on Fe3O4 magnetic nanoparticles (MNPs) and horseradish peroxidase with graphene-chitosan composite material as a matrix. Fourier transform infrared spectroscopy and transmission electron microscopy were applied for the characterisation of the obtained Fe3O4 MNPs. The catalytic performance to hydrogen peroxide was further discussed. Experimental results indicated that the biosensor could electrocatalyse the reduction of H2O2, the reduction peak current exihibited a good linear relationship with the concentration of H2O2 from 2.49x10’5 to 1.67×10-3mol/L (R=0.9990). The detection limit was estimated to be 3.05×10-6 mol/L (S/N=3) and the biosensor also showed good repeatability.3. A Novel Nanofilm Sensor Based on Poly-(Alizarin Red)/Fe3O4 Magnetic Nanoparticles-Multiwalled Carbon Nanotubes Composite Material for Determination of NitriteA novel nitrite sensor was fabricated by electro-polymerizing alizarin red on the surface of glassy carbon electrode modified with Fe3O4-multiwalled carbon nanotubes composite nanofilm. The change of conductivity during the sensor construction process was researched by electrochemical impedance spectroscopy. Under the optimal experimental conditions, it showed that the proposed sensor exhibited good electrocatalytic activity to the oxidation of nitrite, and the peak current increased linearly with the nitrite concentration from 9.64×10-6to 1.30×10-3 mol/L (R=0.9976) with a detection limit of 1.19×10-6 mol/L. This method is sensitive and accurate with good repeatability.4. A New Nitrite Sensor Based on Au/Fe3O4/Chitosan Composite NanoparticlesFe3O4 magnetic nanoparticles and gold nanoparticles were modified on the glass carbon electrode surface to obtain a novel nitrite sensor with chitosan as the protective film. Experiment results showed that the sensor can electrocatalyze the oxidation of nitrite, and the oxidation peak current increased linearly with the nitrite concentration in the range of 5.00×10-6～2.00×10-3 mol/L (R=0.9996) with a detection limit of 7.10×10-7 mol/L (S/N=3). The sensor exhibited good sensitivity, selectivity and repeatability.5. A Novel Nitrite Sensor Based on Fe3O4 Nanoparticles-Multiwalled Carbon Nanotubes Composite MaterialA novel nitrite sensor was constructed via electro-polymerization of L-cysteine on the multiwalled carbon nanotubes and then immobilization of cationic poly (diallyldimethylammonium chloride) coated Fe3O4 nanoparticles through electrostatic assembly at glassy carbon matrix. This sensor exhibited good electrocatalytic activity to the oxidation of nitrite, a new method for nitrite detection was established based on it. The peak current increased linearly with its concentration from 7.49×10-6 to 3.33×10-3 mol/L (R=0.9998). The detection limit was 8.46×10-7 mol/L (S/N=3). Moreover, the sensor exhibited good repeatability, easy preparation and low cost with potential application.