The present work reports for the first time a preparation of reduced graphene oxide (rGO) via a gas-phase process where a visible light photocatalytic reduction of GO with the use of gold (Au) nanocrystals was performed in a single-pass configuration. Primary Au crystals (similar to 4 nm in diameter) were quantitatively incorporated with GO (similar to 36 nm in lateral dimension) in the form of Au-GO hybrid nanoflakes (similar to 37 nm in lateral dimension). The hybrid flakes were then photocatalytically reduced into a form of Au-rGO, and thus the size and structure of the hybrid flakes were reduced (similar to 32 nm in lateral dimension) and changed (the ratio between the D and G bands increased from 0.82-1.10). The Au-rGO hybrid flakes were finally employed to degrade dye and transfect into cells in vitro, and the ability to achieve dye degradation and gene transfection was greater than that of commercial materials. (C) 2013 Elsevier B.V. All rights reserved.