A Lawsone–DAMN based colorimetric chemosensor for rapid naked-eye detection of mercury(ii)

Abstract

We designed and synthesized a new colorimetric chemosensor L based on the combination of 3-hydroxy-1,4-dioxo-1,4-dihydronaphthalene-2-carbaldehyde 2 and diaminomaleonitrile 3 moieties. The recognition abilities of the probe with a range of metal ions were evaluated and their optical properties have been systematically investigated. Chemosensor L exhibited well defined naked-eye visible color changes from yellow to pink for Hg²⁺ detection in acetonitrile. Other ions, including Na⁺, Ca²⁺, CO²⁺, Ni²⁺, Cu²⁺, Mn²⁺, Sn²⁺, Hg²⁺, Fe³⁺, and Th⁴⁺, had a negligible influence on the probe behaviour. The limit of detection (LOD) was 1.1 × 10⁻⁷ M using the UV-vis changes. For the selective recognition of Hg²⁺ ions, it forms a 1 : 1 stoichiometric complex involving naphthoquinone hydroxyl and diaminomaleonitrile nitrogen functionalities. The complex formation was proposed to be in a 1 : 1 ratio based on Job's plot, ¹H NMR titrations, ESI-mass spectrometry analysis and DFT calculations. Test strips based on L were fabricated, which could act as convenient and efficient Hg²⁺ test kits. The results consistently indicated that Lawsone–DAMN is an ideal sensor, which can be utilised to monitor Hg²⁺ in solution over a wide pH range.