A very simple and effective approach of fabricating Au-reduced graphene oxide (Au-RGO) nanocomposite is herein reported. The nanocomposite was synthesized through a one-pot in situ reduction of graphene oxide (GO) and HAuCl4 under ultraviolet (UV) irradiation without using any additional chemical reducing agents, capping agents, stabilizer or surfactant. The surface characterization with various techniques such as UV-vis spectroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and transmission electron microscopy (TEM) showed that GO was effectively reduced and Au nanoparticles with a uniform size were well dispersed on the surface of RGO. This UV light assisted synthesis of Au-RGO nanocomposite is expected to be a universal and clean approach for the formation of various RGO-based nanocomposites. Significantly, the as-prepared nanocomposite possessed high activity in the redox behavior of As (III). Based on the Au-RGO nanocomposite modified electrode, a simple, sensitivity and selective sensing platform for the detection of As (III) was developed. Under optimum conditions, a detection range of 0.3-20 ppb and a low detection limit of 0.1 ppb were obtained, which is found to be well below the World Health Organization (WHO) guidelines of 10 ppb. (C) 2014 Elsevier Ltd. All rights reserved.