Development Of New Graphene-based Materials, Dna Biosensors

DNA biosensor is an important means of analysis and detection of DNA structure using the highly specific biological recognition process between the probe and the target analyte. The rapid identification and detection to specific sequence DNA are followed the specificity complementary pairing rule of DNA molecules to obtain the measurable information output on redox markers. Effective DNA signal sensing system can be applied in biomedical engineering, disease prevention and treatment, research and development of new food, environmental monitoring and control, and other research fields. Therefore, it is very important that the preparation of a fast, portable, sensitive bio-sensors to achieve real-time monitoring of the process of gene expression and the determination of the nature of the product of gene expression.Graphene, as a new form of carbon, is a single-atom thick, two-dimensional sheet of sp2 bonded carbon. Due to its high surface area, excellent electrical conductivity and electron mobility at room temperature, robust mechanical properties, and flexibility, graphene is an ideal material for the preparation of electrochemical sensors and biosensors. It possesses most of the advantageous properties of carbon nanotubes without carrying the most challenging element of carbon nanotube materials-that is, residual metallic impurities, which present the obvious advantages on the electrochemical application. Graphene has a very good development prospects in the field of biosensors, due to the biological compatibility.In this paper, we combined layer-by-layer self-assembly technique with graphene, and then applied them in electrochemical biosensors. The two main aspects of ideas for the research were described as following:(1) because of the function of carrier and excellent efficiency to promote electron transfer, and its good biocompatibility, we fabricate electrochemical biosensors with graphene to get higher-selectivity and larger response signal, (2) studies on the application and efficiency of layer-by-layer modification system consisted of graphene and other materials in the preparation of electrochemical biosensors. With this in mind, four aspects of the work in the present theses have been carried out:1 A Novel Electrochemical DNA Biosensor Based on Graphene and Polyaniline NanowiresA novel DNA biosensor based on oxidized graphene and polyaniline nanowires (PANIw) modified glassy carbon electrode was developed. The resulting graphene/ PANIw layers exhibited good DPV current response for the complementary DNA sequences. The good electron transfer activity might be attributed to the effect of graphene and PANIw. Graphene and PANIw nanolayers film with highly conductive and biocompatible nanostructure were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The immobilization of the probe DNA on the surface of electrode was largely improved due to the unique synergetic effect of graphene and PANIw. Under optimum conditions, the biosensor exhibited a fast amperometric response, high sensitivity and good storage stability for monitoring DNA. The current response of the sensor increases linearly with the concentration of target from 2.12x10-6 to 2.12x10-12 mol 1-1 with a relative coefficient of 0.9938. The detection limit (3o) is 3.25×10-13 mol1-1. The results indicate that this modified electrode has potential application in sensitive and selective DNA detection.2 A DNA Biosensor Based on Graphene Paste Electrode Modified With Prussian Blue and ChitosanA chemically modified graphene paste electrode was prepared by appropriate amounts of graphene in a paste mixture, and followed by electrodepositing of Prussian blue (PB) and chitosan on the electrode surface. The electrode was able to bind ssDNA, and gave a better voltammetric response for complement DNA than did ordinary carbon paste electrodes. The response was characterized with respect to paste composition, the immobilization time of probe DNA on the Chitosan and PB modified graphene paste electrode, and the effect of 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC). The electrochemical behavior of PB assembled on the graphene paste electrode was investigated. The combination of graphene and PB can enhance the current response graphene paste electrode. As a consequence of DNA hybridization, the significant change in the current due to daunomycin intercalated with double-stranded DNA (ds-DNA) on the surface of graphene paste electrode were observed.3 A sandwiched Immunosensor based on Graphene Film Labeled by DNA for the assay of SKOV-3 cellsWe describe herein the combination of electrochemical immunosensors using graphene sheets with a labeled antibody-ssDNA bioconjugates for highly sensitive detection of a cancer biomarker. The immunosensor was constructed by coating graphene film captured antibodies (Ab1) on the surface of glassy carbon electrodes. After antigen (SKOV-3 cells) attached the Ab1, the ssDNA-labeled antibodies (Ab2) were adsorbed to the antigen. Graphene in sandwiched immunosensor can amplify the detectable signal for the SKOV-3 cells. Using SKOV-3 cells as model analytes, the detection limit of the designed immunosensor was 2.9 cells ml-1. The proposed graphene immunosensors show excellent promise for clinical screening of cancer biomarkers and point-of-care diagnostics.4 A Novel DNA Biosensor Modified with Hollow Gold NanoparticlesA novel DNA biosensor was fabricated by modifying ssDNA, cytochrome c, L-cysteine, novel material hollow gold nanoparticles and Chitosan on the surface of glassy carbon electrode. The hollow gold nanoparticles(HGNs) were characterized by Violet spectroscopy and transmission electron microscopy.The behavior of the DNA biosensor was investigated by circle voltammetry, impedance spectrum.The mor-phologic differences among each layer of the DNA biosensor were also observed by atomic force microscope. Results revealed that the amount of adsorbed DNA was 1.672x10-10 mol cm-2. It could be concluded that the modified electrode could be used to detect DNA in the event of hybridization with the indicator daunomycin by differential pulse voltammetry (DPV).