A simple and rapid mercury ion selective electrode has been well constructed. The Au/1-UDT electrode for sensing Hg2xA0;+ has a sensitivity of 28.83xA0;±xA0;0.4xA0;mV/−xA0;pC. The ISE method has a detection limit of Hg2xA0;+ down to 4.5xA0;×xA0;10−xA0;9xA0;molxA0;L−xA0;1. A mechanism with density functional theory for recognition of Hg2xA0;+ is developed. The quantum chemical computation demonstrates Au-Hg metallophilic interaction.