The Diffusive Gradient in Thin films (DGT) technique allows the determination of the ‘labile” metal fraction considered to be more representative of the potentially bioavailable fraction than the dissolved fraction. However, classical DGT based on a polyacrylamide diffusive gel and a Chelex resin do not allow trapping mercury (Hg). Consequently, the development of a combined passive sampling method with GC-ICP-MS is necessary to measure low levels of inorganic mercury Hg(II) and methylmercury (MeHg) in freshwaters. We developed a home-made Hg-specific passive sampler based on an agarose diffusive gel and a 3-mercaptopropyl functionalized silica resin in clean room conditions. It was tested in laboratory and compared to commercial DGT (spheron-thiol) before in situ deployment. We obtained lower level of blank (0.03 ng Hg) in home-made DGT compared to commercial DGT (0.80 ng Hg) resulting in significant quantification limit improvement. The diffusion coefficients determined from kinetic experiments in the home-made agarose gel were 3.74.10-6 and 2.75.10-6 cm²/s for Hg(II) and MeHg, respectively. We demonstrated an efficient measurement of the Hg trapped by the home-made resin by GC-ICP-MS after acidic extraction, isotopically Hg enrichment and derivatization. Hence, the deployment of DGT is proved to be a useful tool applicable in weakly contaminated river. First results showed around 0.2 ng/L of HgDGT in the Bourbre River after 2 weeks of deployment.