Nowadays, the development of a multifunction system for the simultaneous multiple signal amplification detection and fast removal of Hg²⁺ remains a major challenge. Herein, we for the first time used gold nanoparticles (Au NPs) and the corresponding filter membrane as chemosensors and adsorbents for dual signal amplification detection and fast removal of Hg²⁺. Such a system was based on the formation of gold amalgam and a gold amalgam-based reaction between rhodamine B (RhB) and NaBH₄ with fluorescence and colorimetric sensing functions. When the gold amalgam catalyzes the reduction of RhB, the red color and orange fluorescence of RhB gradually changed to colorless by switching the amount of Hg²⁺ deposited on 13 nm Au NPs. The detection limit of the fluorescence assay and colorimetric assay is 1.16 nM and 2.54 nM for Hg²⁺, respectively. Interestingly, the color and fluorescence of RhB could be recovered when the above colorless reaction solution was exposed to air for about 2 hours. Taking advantage of the above optical phenomenon, a recyclable paper-based sensor has been developed by immobilizing the Au NPs and RhB dye on filter paper and has been successfully used for detection of Hg²⁺ in real water samples. In addition, the filter membrane immobilized Au NPs could allow fast removal of mercury ions in Yellow river water and tap water with the removal efficiency close to 99%.