Mercury (Hg) is highly toxic metal originating from natural sources and mainly from anthropogenic processes. It can bioaccumulate all along the food chain and causes severe diseases being thus lethal. Thus, it is of critical importance to ensure continuous Hg(II) monitoring for health and environmental protection. Classical Spectroscopic techniques are routinely used for Hg(II) determination. Although they offer good sensitivity and selectivity, they involve complex procedures and expensive material, which limit their use for on-site analysis. In this context, electrochemical sensors present excellent candidates for in situ Hg(II) trace analysis, taking in account their numerous advantages compared to spectroscopic techniques: easier handling, simple procedure, low energy consuming, low cost material and portability. This work presents a new electrochemical approach aiming to conceive and optimize an electrochemical Hg(II) sensor based on the functionalization of a glassy carbon electrode with gold nanoparticles (AuNPs) and diazonium salts in order to enhance the sensor lifetime. The gold nanoparticles were directly electrodeposited on the glassy carbon electrode, previously functionalized by diazonium salts. The mixed interfaces were then characterized using different electrochemical and spectroscopic techniques. An activation step was finally performed prior to mercury detection. The analytical performances of the sensor (stability, sensitivity, selectivity) towards mercury detection were evaluated using different amounts of Hg(II).