A quinoline-based chromogenic and ratiometric fluorescent probe for selective detection of Mg2+ ion: Design, synthesis and its application in salt lake brines and bioimaging

Abstract A fluorescent probe was rational designed and prepared to distinguish Mg2+ ion from Ca2+ ion, in which 8-hydroxyquinoline acted as not only a fluorophore but also a recognition group. Notably, this probe QB (8-hydroxyquinoline-5-benzothiazole) shows two fluorescence response modes for highly selective detection of Mg2+ ion, namely fluorescence ratiometric mode and turn-on mode, which can be realized by controlling the excitation wavelength at 356 nm or 425 nm. After the addition of Mg2+ ion, the color of the QB solution changed from colorless to yellow, which can be easily found by naked eye. All experimental results suggested that probe QB has a high selectivity toward Mg2+ ion in the presence of other cations. Its detection limit for Mg2+ ion was estimated as low as 0.142 μM, and this value was far lower than the intracellular concentration (0.5–1.2 mM). The detection mechanism was proposed further by the experiment of 1H NMR titration and theoretical calculation. More significantly, this probe was successfully used to detect Mg2+ ion in brine samples as a quantitative method, and was also applied to detecting and imaging Mg2+ ion in living cells, indicating its great application value in practical use for the detection of Mg2+ ion.