The Study Of Food Safety Electrochemical Sensor Based On Novel Nanocomposite Materials

Food comes first to human, so does safety to food. Food safety has always been a major issue relating to the livelihood of the people. Therefore, it is necessary to develop a fast and sensitive method for the detection of harmful substances in food. Electrochemical sensor has the advantages of high sensitivity, good stability, easy operation, simple equipment, and so on. In this paper, four kinds of electrochemical sensors were prepared based on the excellent properties of novel nanocomposite materials, and their application in food safety analysis was focused on. The detailed work is as follows:1. MnO₂ catalysts with morphologies of nanoflowers, nanorods, nanotubes, nanoplates, nanowires and microspheres were prepared via facile hydrothermal synthesis and precipitation methods. By simply grinding with graphene oxide （GO）, MnO₂ could be readily dissolved in water with high solubility and stability due to a large number of hydrophilic groups on the GO surface. The structures, morphologies and electrochemical performances of these as-prepared MnO₂-GO hybrids were fully characterized by various techniques, which were used as sensing material for the simultaneous determination of guaiacol and vanillin for the first time. It was found that the electrochemical properties of the composites were closely related to their morphologies. However, nanoflower—like MnO₂ was more favorable for electron transfer due to its high purity, good crystallinity and unique porous structure, so it showed enhanced electrocatalytic activity and relatively high sensitivity after being combined with GO.2. Being inspired by the relationship between electrochemical behaviors of MnO₂ and its morphology, we found that when the valence state of Mn changed, it had more changes about its three-dimensional structure. Next, we have successfully synthesized various Mn2O3 hollow structures with the morphologies of spheres, cubes, ellipsoids and dumbbells through a suitable manganese source and synthesis method. The water dispersion and stability of Mn2O3 were greatly improved by combining with GO. The composite was characterized by a variety of methods, such as scanning electron microscopy （SEM）, transmission electron microscopy （TEM）, X-ray powder diffraction （XRD）, Raman spectroscopy, Fourier transform infrared spectroscopy （FTIR） and X—ray photoelectron spectroscopy （XPS）. And the Mn2O3-GO was used as the sensor material for the simultaneous determination of food preservative 2-phenyl phenol and butylparaben. The results showed that the electrochemical properties of the composites were not only related to the morphologies of Mn2O3, but also closely related to its hollow structure. Among them, ellipsoids-like Mn2O3 with smaller size and larger specific surface area exhibited stronger electrocatalytic activity. Based on this, a new electrochemical sensor was constructed. The linear range for the determination of 2-phenyl phenol and butylparaben were 0.05～40 μmol/L and 0.05～40 μmol/L, respectively, and the detection limits were 16.3 and 18.8 nmol/L, respectively. In addition, the practical analytical application of the sensing platform was assessed by the determination of 2-phenyl phenol and butylparaben in real food samples with satisfactory results.3. In recent years, functional nanomaterials with core-shell structure have received extensive attention. The Ag@C microspheres with core-shell structure were prepared by a simple hydrothermal reaction, and the effect of Ag source concentration on the resultant stability and sphere sizes was investigated. The results of SEM and TEM showed that when the concentration of Ag source increased from 0.01 mol/L to 0.1 mol/L, the size of Ag@C increased from 130 nm to 2 μm gradually, and the diameter of Ag core and the thickness of carbon shell increased simultaneously. The face-centered cubic Ag phase was presented by XRD and the electrochemical impedance spectroscopy （EIS） data indicated that the conductivity of Ag@C changed with its sizes. Thereafter, a series of different sized Ag@C catalysts were used for the electrochemical sensing of bisphenol A （BPA）. The results showed that Ag@C spheres with diameter of about 220 nm were very effective and stable sensing materials for the determination of BPA, which showed good prospects for sensor application.4. As a kind of unique core-shell materials, yolk-shell structured nanoparticles exhibited the characteristics of nanoreactor, which could provide a unique reaction environment, achieve high concentration enrichment of substrate and active sites, and improve the overall efficiency of the sensing material. In this work, yolk-shell structured CuO@SiO₂ microspheres were synthesized via a facile route, which was used as sensing material of electrochemical sensor to study the electrochemical behaviors of Formoterol fumarate （FF）. The results of cyclic voltammetry and square wave voltammetry showed that the fast electrocatalytic oxidation of FF could occur on the CuO@SiO₂ modified glassy carbon electrode and lead to the sensitive determination of FF. Under the optimal conditions, the oxidation current of FF was linear to its concentration in the range of 0.03～10 μmol/L and the detection limit was found to be 5.0 nmol/L （S/N= 3）, which demonstrated excellent analytical performance. Finally, the fabricated electrochemical sensor was applied to the selective determination of FF in complicated food samples.