† These authors contributed equally to this workWe report on the enhancement of surface plasmon resonances in a holey bidimensional grating of subwavelength size, drilled in a gold thin film coated by a graphene sheet. The enhancement originates from the coupling between charge carriers in graphene and gold surface plasmons. The main plasmon resonance peak is located around 1.5 µm. A lower constraint on the gold-induced doping concentration of graphene is specified and the interest of this architecture for molecular sensing is also highlighted. † These authors contributed equally to this work.PACS numbers: 78.67. Wj, 73.20.Mf, 42.79.Dj, 07.07.Df Plasmonic devices offer valuable platforms for a wide range of emerging molecular detection schemes. Among such applications, biosensors are very promising especially from the point of view of lab-on-a-chip (LOC) technologies. 1 Indeed, plasmon resonances are characterized by both a strong electric field and a great sensitivity to environmental conditions. As a consequence, adsorbed species can be detected through the resonance wavelength shift. In addition, the strong electric field enhancement allows for surface enhanced Raman spectroscopy, which can be used for single molecule detection. 2 Surface plasmons (SPs) require specific conditions to be excited. For instance, in the Kretschmann configuration, a light beam is totally internally reflected in a prism on which a metallic film is deposited and triggers the generation of SPs. 3 In a holey metal film, SPs can be excited by a normal incidence light beam. 4 Light is scattered due to the corrugations and the evanescent diffraction orders can excite SPs. 5 For a metallic layer accommodating an array of holes with subwavelength size, it is possible to probe SPs by simply measuring the intensity of the transmitted light. Such a simple configuration is much more practical in the LOC context and it has been widely studied since the pioneering work of Ebbesen et al. in 1998. 4 Recent theoretical works have shown that doping can induce SP modes in graphene. 6-8 Graphene, which appears as a monoatomic layer made of sp 2 carbon atoms in a hexagonal lattice configuration, presents a plethora of amazing properties. 9 In that context, SPs have been observed for graphene doped by charge transfer from metal thin films, 10-13 external atoms 14 or electrostatic gating 15,16 . It has been also suggested that SPs could be excited in graphene on a periodically structured * e-mail: michael.sarrazin@unamur.be substrate 17,18 or via regular patterns in graphene. [19][20][21][22][23][24][25] A recent experimental result showed that graphene SPs can be excited in a Kretschmann configuration using graphene deposited on a planar gold layer. 10 A different approach 26 was used in which SP resonance tunability was achieved by electromagnetic field coupling between a graphene sheet and SPs excited in gold nanoparticles.In the present work, we describe and study an opti-