| Due to its easy preparation, low cost, high sensitivity, excellent selectivity andhigh stability, the electrochemical sensor has been widely applied in health care, foodindustry, agriculture, environment and so on. Since the characteristics of theelectrochemical sensor greatly relys on the materials modified on the electrodes, inorder to improve the performance of the sensors, developing suitable electrodematerials is one of the most interesting projects. Graphene, a two-dimensional newcarbon material, is a single-atom thick sheet of sp2bonded carbon. Due to its highsurface area, excellent conductivity, good electron mobility at room tempreture, robustmechanical proerties and flexibility, graphene is an ideal material to modify theelectrodes. In this study, an electrochemical DNA sensor based on electrochemicallyreduced graphene oxide (ERGO) was developed and then applied in the evaluation oftotal antioxidant capacity (TAC). In addition, the van der Waals interactions among thegraphene sheets can result in their tendency to form irreversible agglomerates or evenrestack to form graphite, which will greatly restrict the application of graphene inelectrochemical sensors. Therefore, a hierarchical nanostructure using hollownitrogen-doped carbon spheres (HNCS) as nanospacers to separate reduced grapheneoxide nanosheets (RGO) was prepared and then applied in the research on theelectrochemical sensor. The main points of this thesis are as follows:(1) The electrochemical DNA sensor was constructed by electrochemicalimmobilization of guanine on ERGO modified glassy carbon electrode. The resultsindicate ERGO not only greatly enhances the load of guanine on the electrode butalso promotes the electrochemical oxidation of guanine, because of its its highsurface area and excellent conductivity. Moreover, the electrochemical DNAsensor was applied in the evaluation of total antioxidant capacity (TAC) in somecommercial fruit juices. And a Fenton reaction was used to induce guanineoxidative damage by hydroxyl radicals(OH), which decreased the oxidationcurrent of guanine, and ascorbic acid (AA), a powerful antioxidant, was used toprotect guanine from oxdative damage. Thus, we detected the concentrations ofantioxidant AA by means of changes in the guanine anodic peak current obtainedby square wave voltammetry (SWV). The electrochemical DNA sensor exhibitswide linear range (1.00-20.00mg L-1), low detection limit(0.24mg L-1), high reproducibility and strong anti-interference ability.(2) By the electrostatic self-assembly between the positively charged polydopaminewrapped SiO2(SiO2@PDA) and the negatively charged graphene oxide (GO), aSiO2@PDA-GO hierarchical nanostructure was successfully fabricated. Afterheat-treatment and HF etching, a HNCS-RGO hierarchical nanostructure usinghollow nitrogen-doped carbon spheres (HNCS) as nanospacers to separate reducedgraphene oxide nanosheets (RGO) was obtained. The morphology and thecomposition of the HNCS-RGO hierarchical nanostructure were studied byscanning electron microscopy (SEM), transmission electron microscopy (TEM)and energy dispensive spectroscopy (EDS). And the electrochemical behavior ofthe HNCS-RGO hierarchical nanostructure modified electrode was investigated bycyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS).Then, the HNCS-RGO hierarchical nanostructure was applied in simultaneouselectrochemical determination of ascorbic acid (AA), dopamine (DA) and uricacid (UA). The results show that the high electric conductivity, nitrogen-dopingeffect and unique hierarchical nanostructure of the HNCS-RGO have significantlypromoted the electrochemical oxidation of AA, DA and UA on the electrode. Theelectrochemical sensor shows wide linear range (AA:50-1200M; DA:0.5-90M; UA:1-70M), low detection limit (AA:650nM; DA:12nM; UA:18nM),good reproducibility and high stability. Finally, it was successfully used forsimultaneous determination of AA, DA and UA in human urine samples.(3) An electrochemical sensor based on the HNCS-RGO hierarchical nanostructurewas fabricated for the determination of nicotinamide adenine dinucleotide(NADH). Compared with the bare glassy carbon electrode (GCE) and the RGOmodified glassy carbon electrode (RGO/GCE), the HNCS-RGO hierarchicalmaterial modified glassy carbon electrode (HNCS-RGO/GCE) shows higheroxidation current (94.0A) and lower oxidation potential (+0.19V vs. SCE)towards the oxidation of NADH. Therefore, the electrochemical sensor was usedfor determination of nicotinamide adenine dinucleotide (NADH).The results showthat the HNCS-RGO/GCE has low detection limit (0.015μM), wide linear range(0.1-900μM), high stability and strong anti-interference ability. |
