The Preparation Of Graphene Modified Electrode And The Detection Of Small Biomolecules

Graphene, as a single layer of carbon atoms in a closely packed honeycomb lattice, is a two-dimensional carbon nanomaterial. Due to the properties of good conductivity and huge surface to volume ratio, graphene has been attracted considerable attention from materials chemistry and electrochemical chemistry in recent years. Topreparestable aqueous dispersions of graphene with low cost, high effectivelyis very important tofabricate graphene modified electrode conveniently, fast and cheaply. Graphene modified electrode can promote the electron transfer more effectively between the target molecules and the electrode than the non-modified electrode. Therefore, graphene modified electrode has potential application in electrochemical analysis of bio-analytes.In this paper, graphene was prepared by chemical exfoliation from pre-oxidized carbon powder. The obtained graphene which contained oxygen-containing functional groups can be dispersed in water well. Productive time could be shortened and the yield could be increased by controlling temperature through the recation process. Graphene modified glass carbon electrode can be fabricated easily by drop-casting graphene dispersion onto the substrate electrode surface. Electrochemical reduced method and doping method were employed for improving the electrical conductivity and electrochemical activity of graphene film. Several kinds of small biomolecules were detected successfully at the graphene modified electrode. The main results obtained in this work are as follows:1. Graphene was prepared by chemical exfoliation from pre-oxidized carbon powders. The experimental results indicate that the proposed method exhibit some superiority because it can effectively increase the oxygen-containing functional groups in short preparation time andwell-dispersed graphene aqueous solution.2. Electrochemical reduced graphene electrode(ERGO/GCE) was in situ prepared successfully by electrochemical reduction.Graphene modified glass carbon electrode(GO/GCE) was prepared firstly by drop casting method from graphene dispersion. Then, the obtained GO/GCE was reduced to fabricate ERGO/GCE by constant potential method in phosphate buffer saline(PBS). The oxygen content in ERGO film was decreased obviously during the reduction process. Additionally, a lower charger transfer resistance and higher electrochemical activity were obtained at the ERGO/GCE. The optimal condition to fabricate ERGO/GCE was reduction of GO/GCE at the potential of-1.3 V(vs. SCE) for 300 s.3. Cyclic voltammetry and differential pulse voltammetry were used to investigate the electrochemical behaviour of adenine(Ade) at ERGO/GCE. Compared with GCE and GO/GCE, Ade can be oxidized more easily and the oxidized current of Ade was increased greatly at ERGO/GCE. The electro-oxidation of Ade at ERGO/GCE was identified to an irreversible, adsorption-controlled process and involve two electrons and two protons. The plot of oxidation current versus Ade concentration showed two linear segments in the concentration ranges 1 to 7 μM and 7 to 50 μM, respectively. The detection limit was calculated to be 0.12 μM(S/N=3).4. The electrochemical response of guanine(Gua) at ERGO/GCE was investigatedby cyclic voltammetry and differential pluse voltammetry. Based on the good sensitivity and selectivity of ERGO/GCE to guanine, the voltammetric signal of Gua in cell lysates was successfully applied for counting the number of cells. The electro-oxidation of Gua is an irreversible and adsorption-controlled process at ERGO/GCE. Two electrons and two protons were involved in the rate-determining step of guanine electro-oxidation reaction. The oxidation current was increased linearly with increase in Guaconcentration from the range of 0.5 μM to 10 μM. The detection limit was calculated to be 0.25 μM(S/N=3). The oxidation current of Gua was also linearly dependent on the number of cells in cell lysates from the range of 3.52 × 105 to 1.27 × 107 cells·mL-1. The detection limit was 1×105 cells·mL-1.5. Gua and Ade could be detected simultaneously in DNA at ERGO/GCE. Both of the oxidation current were linearly dependent on the concentrations of Gua and Ade in the range of 0.5- 10 μM and 2.5- 50 μM, respectively. The detection limit was 0.15 μM for Gua and 0.10 μM for Ade(S/N=3) in 50 mM PBS(pH 6.86). The ERGO/GCE was also successfully applied for simultaneous detection of Gua and Ade in thermally denatured herring sperm DNA. The result(Gua/Ade = 0.758) indicates that the proposed ERGO/GCE provides a promising potential for simultaneous detection of Gua and Ade in real samples.6. A novel gold(Au) nanoparticles, poly(caffeic acid)(PCA) and graphene composite modified GCE(Au/PCA/PGOM/GCE) was prepared. Compared with PGOM/GCE, the Au/PCA/PGOM/GCE electrode exhibited an excellent electrocatalytic activity and conductivity by successively potentiostatic deposition of PCA and Au nanoparticles.7. Electrochemical behaviors of acetaminophen(AP) at the Au/PCA/PGOM/GCE was investigated by cyclic voltammetry and differential pluse voltammetry. The application of the Au/PCA/PGOM/GCE electrode as electrocatalytic sensors in the voltammetric detection of AP in real samples was also illustrated. Two electrons and two protons were involved in the rate-determining step of AP electro-oxidation reaction at the electrode. The electrochemical processes of AP at the Au/PCA/PGOM/GCE was controlled by adsorption and diffusion simultaneously. The detection limit was 0.005 μM. The Au/PCA/PGOM/GCE has been successfully applied and validated by analyzing AP in blood, urine and pharmaceutical samples.