Researchers have been looking for novel materials to improve the performance of photonic devices. Graphene has great potential to optoelectronic applications because of its excellent optical properties. Here, we demonstrate using the graphene-based photodetectors for infrared detection under a zero-bias operation. We have demonstrated to use an electricfield-assisted method to manipulate graphene flake between metal microelectrodes successfully without the electron beam lithography. The devices are made from few-layer-graphene and multi-layer-graphene which are confirmed by Raman spectroscopy and atomic force microscopy. The size of the graphene flake can be as large as 15 μm x 15 μm. The obtained results demonstrate high potential applications of the electricfield-assisted technique and nano assembly to fabricate graphenebased infrared photodetectors.