Preparation Of Functional Graphene Modified Electrodes And Its Application In Electrochemical Analysis

Due to the unique structure and excellent performance, the study of graphene has been expanded globally since it was reported by Geim who was in the University of Manchester in 2004. The excellent electrical and physical properties of graphene, maked it plays an important role in electrochemical analysis. However, in practical applications, in order to make full use of its excellent properties, graphene must be functionalizd effectively. Not only can functionalized graphene maintain the original performance, but it can also exhibit reactivity of the modified group.This makes it possible for graphene reaction and dispersion. Now functionalized graphene can be divided into non-covalent functionalization and covalent functionalization, and these two methods have its own advantages and disadvantages, but they are all essential to the optimization of graphene’s performance. Functionalized graphene composite can be used to modify electrodes, and it is widely used in the field of electrochemistry. The electrochemical method is an effective means to the detection of small biological molecules. Since a variety of small biomolecules always coexist in the same system, simultaneous detection will become the research goals to many researchers. Functionalized graphene composite material with the reactivity of the modified group helps to measure a variety of small biomolecules simultaneously.In this study, we investigated the functionalization of graphene mainly including covalent functionalization and noncovalent functionalization. And used the functionalized graphene composites to modify the electrodes and then studied the electrochemical behaviors of some small biological molecules(such as dopamine, uric acid, amino acids, purine, etc.) at the modified electrode surface. The works are as follows: 1. Preparation of PEI-G modified glassy carbon electrode and its application for simultaneous detection of ascorbic acid, dopamine, uric acid and tryptophanIn this work, PEI functionalized graphene was prepared with Covalent bonding method. The reaction mechanism of PEI–graphene composite is a covalent grafting process of PEI to the graphene sheets through the nucleophilic ring-opening reaction of epoxy groups in graphene oxide with the amino groups in PEI. Using this composite material to modify GCE makes the simultaneous detection of AA, DA,UA and Trp become available. In the coexisting system of AA, DA, UA and Trp,the differences of the oxidation peak potential of AA-DA, DA-UA, UA-Trp were 298 m V,130 m V,and 350 m V, respectively. During the detection of AA, DA, UA and Trp, the linear ranges were 50- 5800 μM, 30-2570 μM, 0.05- 400 μM and 6- 1000 μM, with the detection limit of 16.67 μM, 10 μM, 0.017 μM and 2 μM, respectively. 2. Preparation of PDDA-G modified GCE and its application for selective detection of tryptophan.We used Hummers method to synthesize graphite oxide firstly,then using hydrazine hydrate as its reducing agent, at the same time, positively charged(PDDA) was also used to synthesize PDDA functionalized graphene(G)(PDDA-G). The application of this composite material for modifing GCE, making the selective detection of tryptophan become available. The result suggested that tryptophan has a good electrochemical response in a wide linear range of 0.06-150 μM, and the detection limit was 0.019 μM(S/N=3). 3. Preparation of PDDA-G/MWCNT modified GCE and its application for simultaneous detection of xanthine, hypoxanthine and uric acidIn this work, positively charged(PDDA) was first used to synthesize non-covalently functionalized graphene(G)(PDDA-G). Then, the composite material was sonicated with CNT to synthesize PDDA-G-CNT. The application of this composite material for modifing GCE helped to detect xanthine, hypoxanthine and uric acid, simultaneously. The oxidation peak current of xanthine was linear with its concentration in the range of 0.05-75 μM with the detection limit of 0.016 μM(S/N=3). The oxidation peak current of hypoxanthine was linear with its concentration in the range of 0.1-125 μM with the detection limit of 0.033 μM(S/N=3). The oxidation peak current of uric acid was linear with its concentration in the range of 0.1-65 μM with the detection limit of 0.033 μM(S/N=3).