New phenanthridine-based multi-functional chemosensor for selective detection of Th4+ and Hg2+ ions in both aqueous and solid state

A new phenanthridine-based multifunctional chemosensor (L), was synthesised via a green synthetic route and characterised using FT-IR, NMR and HRMS analysis. The sensing application of L towards metal ions in both solution and solid-state was studied using UV–vis and fluorescence spectroscopy, which exhibits dual-sensing behaviour for Th⁴⁺ and Hg²⁺ ions with good recyclability. In aqueous acetonitrile, L showed rapid response for the detection of environmental toxic metal ions and has a very low analytical detection limit of 125.5 pM and 1.94 nM for Th⁴⁺ and Hg²⁺ions respectively, which is remarkably lower than the World Health Organization standard. The cation binding property of the L with Th⁴⁺ and Hg²⁺ions was investigated by Job plot, ¹H NMR titration, HR-MS and DFT calculation. The in-situ formed ensemble L-Hg²⁺ was further applied in the naked-eye detection of Cys (Cystine) and His (Histidine) over other common amino acids. The utility of L for real-time detection of Hg²⁺ and Th⁴⁺ ions was explored in various sources of environmental water samples, test paper strips, fingerprint imaging, fluorescent ink and smartphone-assisted sensing techniques, demonstrating the promising on-site visualization of the probe in controlling the toxicity levels in wastewater sources without resorting to expensive instruments.