Indolenine-based semisquaraine dye for visual detection and sensing of mercury (II)

Mercury is a highly toxic pollutant that poses significant risks to the environment and human health. Despite the availability of various methods for detecting Hg2+ ions, there is a high demand for the development of small molecule sensors that are simple, rapid, cost-effective, selective and sensitive. Here, we examine the application of indolenine-based semisquaraine dye SqS as a chemosensor for the mercury detection in an aqueous and organic (alcoholic) media. The addition of Hg2+ ions to the SqS solution induces a noticeable color change from light pink to yellow, while other metal cations, including Li+, Ni+, Na+, K+, Ba2+, Mg2+, Ca2+, Cu2+, Co2+, Fe3+, Al3+, Pb2+, and Cd2+ do not cause any significant change in color or absorption spectra. The limit of Hg2+ detection under proposed measurement conditions was determined to be 38 nM. The analysis of the binding characteristics of SqS using Job’s and molar ratio methods, along with mass spectrometry, indicates that the stoichiometry of the SqS–Hg2+ complex is 1:1 and 2:1. This chemosensor can be used for the selective colorimetric detection of mercury ions in environmental samples, such as water sources, and in biological systems, contributing to pollution monitoring and safety assessments.