Electrochemical Hydrogen Peroxide And DNA Sensors Using Graphene As Signal Amplification Medium

As a single carbon atom material of the planar structure new carbon materials, Graphene has received a great deal of attention in the field of biological sensing. Based on the special properties of graphene and graphene oxide such as large surface area, high catalytic efficiency and multiple active sites, a series of modified electrodes based on graphene oxide or graphene and its composite materials were prepared, and those were applied to determination of hydrogen peroxide and oligonucleotides. Some new types of electrochemical sensors were constructed. The main contents are as follows:(1) A graphene oxide(GO) modified glassy carbon electrode(GO/GCE) was fabricated by covalent coupling method, and then by immersing electrode circlly into K4[Fe(CN)6] and Fe Cl3 solution the Prussian blue(PB) was in-situ growth on the surface of the GO/GCE, after direct electrochemical reduction of GO to reduction types of graphene oxide(EGR), and coating with stable Nafion, So far, a novel hydrogen peroxide sensor was obtained. In acid media, the electrocatalytic property of the assembled sensor for hydrogen peroxide was investigated by cyclic voltammetric and amperometric methods. The results showed that the sensor of Nafion/PB/EGR/GCE exhibited excellent electrocatalytic property for hydrogen peroxide analysis at the optimized potential condition, and the catalytic current presents a good linear relationship with concentrations of the hydrogen peroxide in the range from 5.0×10-6 mol/L to 1.0×10-3 mol/L with a low detection limit of 2.0×10-6 mol/L, based on the signal-to-noise characterific(S/N = 3). The sensor also could prevent interference from ascorbic acid(AA), dopamine(DA), citric acid and glucose.(2) A novel impedance type electrochemical DNA sensor was constructed based on in-situ chemical reduction of GO at DNA modified electrode. First, the mercapto-modified probe DNA(S1) was anchored on a gold electrode surface according to the Au-S bond. Then GO was adsorbed on the S1 through the unique π-π stacking. At Last, using sodium borohydride in-situ reduction of GO to the ultrahigh charge-transfer efficiency of reduction types of graphene oxide(r GO). Thus, resulting in a very low charge-transfer resistance of the electrode surface to reduce the background response, when the sensor hybridized with the target DNA to form the stable double-strand DNA(ds DNA), r GO was released from the electrode surface, so the charge-transfer resistance increased. The hybridization experimental results demonstrated that this DNA biosensor could detect the DNA target quantitatively and the impedance change values with the target DNA concentration have good linear relationship in the range from 1.0×10-15 mol/L to 1.0×10-9 mol/L, with a limit of detection as low as 2.9×10-16 mol/L. The selectivity experiment showed the sensor exhibited good recognition for one-base, three-base mismatched and non-complementary DNA.(3) The probe DNA with thiol was fixed on the gold electrode surface by simple self-assemble technology. After graphene oxide nanosheets were self-assembled on probe DNA, then using hydroquinone as a reducter, the electroactivity of Ag nanoparticles(Ag NPs) was in-situ anchored on the GO, after that, a novel electrochemical DNA biosensor was construced based on the graphene oxide and Ag NPs compoud. The Morphologic characterization of the step-by-step assembly of the biosensing interface resulted from scanning electron microscope(SEM) and electrochemically characterized via CV and EIS using [Fe(CN)6]3-/4- as the probe. When the sensor hybridized with the target DNA to form double-stranded DNA, GO-Ag NPs compound fell off from the electrode surface, and which caused the sensor signal to attenuation. The analysis performances of the biosensor were investigated by differential pulse voltammetry(DPV) and the result showed the peak currents presented a good linear relationship with the concentrations of the complementary sequences in the range from 1.0×10-14 mol/L to 1.0×10-8 mol/L with a detection limit of 5.6×10-15 mol/L, and exhibited good discrimination ability to the complementary sequences, one-base, three-base mismatched and non-complementary sequences.