A fluorescent pH switch probe for the ‘turn-on’ dual-channel discriminative detection of magnesium and zinc ions

Abstract

A coumarin-based fluorescent probe is presented for the multi-channel reversible “ Turn-on ” detection of Mg 2+ ion (at 483 nm) and Zn 2+ ion (at 560 nm) as well as a base (450 nm) at different wavelengths with large Stokes shifts. • A coumarin-based probe HL is utilized for the dual channel ‘turn-on’ detection of Mg 2+ and Zn 2+ ions. • HL detects Mg 2+ and Zn 2+ ions at two different wavelengths with large Stokes shifts. • HL detects both metal ions by the inhibition of C=N bond rotation, PET and ESIPT while promoting CHEF. • Probe HL also functioned as a reversible fluorescent pH switch. • HL was utilized for the detection of Mg 2+ and Zn 2+ ions in human breast cancer cells. • Low-cost detection methods, paper-strips and polymer films, were used for the sensing of Mg 2+ and Zn 2+ ions. A coumarin-based fluorescent probe, HL (( E )-8-((benzo[d]thiazol-2-ylimino)methyl)-7-hydroxy-4-methyl-2H-chromen-2-one), is presented for the dual-channel “ Turn-on ” detection of Mg 2+ (at 483 nm) and Zn 2+ (at 560 nm) ions at two different wavelengths with large Stokes shifts. HL exhibits impressive detection limits and binding constants with both Mg 2+ and Zn 2+ ions. HL detected these ions by the inhibition of -C=N bond rotation and suppression of photoinduced electron transfer (PET) and excited state intramolecular proton transfer (ESIPT) while promoting chelation enhanced fluorescence (CHEF). For the detection of Mg 2+ and Zn 2+ ions, reversibility was achieved by using ATP. HL is not only sensitive and selective for the detection of Mg 2+ and Zn 2+ ions but also showed considerable reversible “ Turn-on-Turn-off ” fluorescent pH switch behavior. The DFT studies assisted in understanding the binding of Mg 2+ and Zn 2+ ions by the probe. HL was utilized to detect Mg 2+ and Zn 2+ ions in the human breast cancer cell line by fluorescence cell imaging studies while several low-cost detection methods were also illustrated.