In the first section of this study, Thionin (Th), as a mediator for electron transfer, was linked on the surface of graphene oxide by diazonium reaction. Then, carbon paste electrode was modified with the nanocomposite and the charcteristics were studied with different electrochemical methods. The cyclic voltammograms showed that the redox behavior of the modified electrode is diffusion controlled and pH dependent. The modified electrode showed electrocatalytic behavior toward reduction of hydrogen peroxide and oxidation of NADH. The effect of some experimental parameters such as modifier percentage, pH and applied potential were investigated usingamperometery. Under the optimized conditions, amperometric currents were found to be linear with the concentration of hydrogen peroxide and NADH in the range of 2.0 to 3500.0 µmol L -1 and 2.0 to 500.0 µmol L -1 , respectively. The detection limits were found to be as 1.3 µmol L -1 and 0.43 µmol L -1 for hydrogen peroxide and NADH, respectively. The proposed modified electrode showed good repeatability and reproducibility. This method was successfully applied for the determination of H 2 O 2 in real sample. In the second section of this study, a novel, cheap and simple enzymeless glucose and oxygen sensor is introduced based on NiO nanoparticles decorated on Nile blue functionalized reduce graphene oxide (Nile?rGO). Then, it was converted to bimetallic system by galvanic replacement between NiO and Pd nanoparticles (Pd@NiO/Nile?rGO) to prepare a modified carbon paste electrode (CPE). This electrode was prepared by using functionalized graphene oxide with Nile blue through the diazonium reaction and deposition of Pd?NiO nanoparticles with chemical reaction and galvanic replacement. Then, the noncomposite structure was characterized by field emission scanning electron microscopy, X?ray diffraction, fourier transform infrared spectroscopy, energy dispersive X-ray spectroscopy, electrochemical impedance spectroscopy and cyclic voltammetry. Electrochemical studies showed that Pd/NiO@Nile?rGO has higher electrocatalytic activities towards glucose electro-oxidation. Potential cycling test was employed to confirm the stability of the electrocatalyst and the results revealed high sensitivity, high stability of Pd/NiO@Nile-rGO and suitable electrode for fuel cell. A sensitive amperometric detection of glucose is achieved at ?0.040 V ( vs. Ag/AgCl) with a low detection limit of 2.2 ?mol L ?1 and with a wide linear range of 0.020?20 mmol L ?1 . In continue of this work the electrocatalytic activity of the modified electrode for the electro reduction of oxygen has been studied too. Five different Pd/NiO@Nile-rGO/CPEs were tested separately for the amperometric response of glucose, providing a relative standard deviation (R.S.D.) 4.8%. The selectivity of the modified electrode was studied. The applicability of Pd/NiO@Nile-rGO/CPE was investigated by determining glucose in blood serum sample with satisfactory results.