An electrochemical nanogenosensor was developed based on a gold nanoparticles/graphene -chitosan (AuNPs/GR-CS) ternary nanocomposite for detection of the target DNA of H. pylori cagE gene. The nanogenosensor construction processes were investigated by electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) using [Fe(CN)(6)](3-/4-)as a redox probe. The optimum conditions were found for the immobilization of thiolated probe on the nanogenosensor surface and its hybridization with the target DNA. The nanogenosensor is capable of detecting the target DNA from a one-nucleotide change in the target sequence. In optimum conditions, the two linear calibration ranges of 1.0 x 10(-15) to 1.0 x 10(-12) M and 1.0 x 10(-12) to 1.0 x 10(-6) M with a detection limit of 5.0 x 10(-16) were obtained for the target DNA determination using an EIS method. The EIS and differential pulse voltammetry (DPV) were applied to detect the DNA damage induced by UVC radiation. In the DPV method, the methylene blue (MB) signal was used to detect dsDNA damage which is due to UVC radiation. (c) 2016 The Electrochemical Society.