In the first section of this study, reduced graphene oxide (rGO) was used in the preparation of DNA based biosensor and the effect and ability of three flavonols antioxidants ( myricetin, fisetin and kaempferol ) to prevent DNA damage were studied .Acridine orange (AO) was used as a DNA damaging agent because it shows a high affinity to nucleic acid (intercalates into ds-DNA or binds electrostatically to single strain DNA) and stretch of double helical structure of DNA. Here, a simple and inexpensive methodology was used to develop a novel electrochemical biosensor to demonstrate the destructive effect of AO on DNA damage and then for the determination the inhibitory effect of each of the flavonols antioxidants to prevent DNA damage. Decreasing on the oxidation signals of guanine and adenine bases in the presence of AO were used as probes to study the antioxidants power of these flavonols, using the DNA-modified screen printed graphene electrode (DNA/SPGE). The results showed that the DNA-biosensor could be a suitable sensor to investigate the inhibitor ability of the flavonols antioxidants on DNA damage. To confirm the electrochemical results, Uv-Vis and florescent spectroscopy were used too. In the second section of this study, an efficient electrocatalyst for hydrogen evolution has been developed base on electrostatic interaction between poly-diallyldimethylammonium chloride (PDDA) @ rGO, PDDA @carbone nanotube (CNT) and polyoxometalate (here, [PW 11 NiO 39 ] m- ). Also in this work, we apply a new metal deposition method. Galvanic replacement reaction provides a simple and effective method for preparation of noble metals particles including Pt. One advantage of this method is reducing the amounts of noble metal that require for modification of electrodes. Electrochemical properties in 0.5 M H 2 SO 4 solutions have been investigated by the polarization measurement and electrochemical impedance spectroscopy (EIS) technique. The electrodes exhibit high catalytic activity for hydrogen evolution with a low over potential, a high current density, long term stability and retain high catalytic performance.
