A turn-on anthraquinone-derived colorimetric and fluorometric dual-mode probe for highly selective Hg2+ determination and bioimaging in living organisms

Abstract

Mercury ion (Hg²⁺) is considered a harmful neurotoxin, and real-time monitoring of Hg²⁺ concentrations in environmental and biological samples is critical. Fluorescent probes are a rapidly emerging visualization tool owing to their simple design and good selectivity. Herein, a novel fluorescence (FL) probe 2-(4-((6-((quinolin-8-yloxy)methyl)pyridin-2-yl)methyl)piperazin-1-yl)anthracene-9,10-dione (QPPA) is designed using piperazine as a linker between the anthraquinone group, which serves as a fluorophore, and N₄O as the Hg²⁺ ligand. The probe exhibits FL "turn-on" sensing of Hg²⁺ because the complex inhibits the photo-induced electron transfer (PET) process. Moreover, QPPA can overcome the invasion by other possible cations, resulting in a clear color change from orange to colorless with the addition Hg²⁺. The chelation of QPPA with Hg²⁺ in a 1:1 ratio. Subsequently, the theoretically determined binding sites of the ligand to Hg²⁺ are validated through ¹H NMR titration. The in situQPPA-Hg²⁺ complex can be subjected to Hg²⁺ extraction following the introduction of S^2- owing to its robust binding capacity. The exceptional limit of detection values for Hg²⁺ and S^2- are obtained as 63.0 and 79.1 nM (S/N = 3), respectively. Moreover, QPPA can display bright red FL in the presence of Hg²⁺ in different biological specimens such as HeLa cells, zebrafish, onion root tip tissues, and water flea Daphnia carinata, further providing an effective strategy for environmental monitoring and bioimaging of Hg²⁺ in living organisms.

Keywords: Anthraquinone-based probe; DFT studies; Environmental analysis; Imaging; Mercury ion.