The commercialization of graphene requires a new route for its industrial scale production that does not involve high costs, hazardous raw materials, and complex production techniques. Here, we report a simple and cost effective approach for producing highly conductive graphene films by reducing graphene oxide (GO) sheets without high-temperature annealing or any toxic solvent. At 90 C, ionic solutions, such as MgCl2, NaCl, AgNO3, FeSO4, CuCl2, and AlCl3, not only reduce GO but also cross-link adjacent graphene sheets to form reduced GO (Re-GO) films on various substrates. All of the GO-based films show color change from brown to grey and improved electro-conductivities. The as-prepared Re-GO films can directly be prepared onto target substrates without any transfer processes, which keeps the integrity of the films. Electrodes modified by Re-GO metal nanocomposite films present extremely large electro-active surface area and fast amperometric response, which is promising for sensor development. (C) 2014 Elsevier B.V. All rights reserved.