Metal ions are essential for numerous chemical and biological processes;" however, Hg2+ is highly toxic, even at trace concentrations. Therefore, efficient detection of Hg2+ is crucial. Fluorometric detection, using receptorbased sensors, presents a promising approach. In this study, we developed an acridinedione-pyridine-3,5dicarbonitrile-based receptor, ARP, for the sensitive and specific detection of Hg2+. ARP was characterized using FTIR, NMR (1H and 13C), and HRMS, respectively. When compared to other metal ions, the receptor showed significant selectivity for Hg2+, exhibiting a noticeable shift in color from yellowish-brown to light yellow in acetonitrile solution. 1H NMR titrations, HRMS analysis, and DFT calculations were conducted to determine the interaction between ARP and Hg2+ ions. The binding stoichiometry between ARP and Hg2+ was observed to be 2:1, as verified by Job's plot. The limit of detection and quantification for Hg2+ were found to be 19.8 nM and 66.6 nM, respectively. The receptor exhibited a quick response to Hg2+ ions, and EDTA titration studies confirmed its reversibility. ARP successfully detected Hg2+ in real samples, including water, paper strip, and living HeLa cells, demonstrating a reliable and versatile sensor for monitoring mercury contamination in environmental and biological systems."