Rhodamine-Appended Polymeric Probe: An Efficient Colorimetric and Fluorometric Sensing Platform for Hg²⁺ in Aqueous Medium and Living Cells

Nowadays, monitoring of trace amounts of Hg2+ ions in environmental and biological systems has become crucial owing to their detrimental effects on living organisms. To serve this purpose, a rhodamine-affixed water-soluble polymeric probe, CP2, was fabricated to detect Hg2+ ions in water and living cells. The sensing performance toward several competitive cations was assessed via UV–vis spectroscopy and fluorescence spectroscopy, which indicated high selectivity of the polymeric probe toward Hg2+ ions. CP2 showed both colorimetric (colorless to pink to violet) and fluorimetric “off–on” (nonemissive to red fluorescence) responses toward Hg2+ in water at pH 7.0 with a low limit of detection (10.7 nM) and a high binding constant value (7.14 × 107 M–1). The spectral changes were ascribed to Hg2+-induced spirolactam ring-opening of xanthene units present in the polymeric pendant. CP2 readily binds (less than a minute) with Hg2+ ions through a 1:1 irreversible complex formation. For practical applicability, filter-paper-based test strips were fabricated and utilized for naked-eye sensing of Hg2+ ions in water. Moreover, intracellular imaging applications demonstrated high efficiency of CP2 as a biocompatible fluorescent probe to sense Hg2+ ions in glioblastoma cells (U-87).