Simple thiosemicarbazone 'switch' sensing of Hg2+ and biothiols in pure aqueous solutions and application to imaging in lysosomes

A water-soluble salicylaldehyde-based thiosemicarbazone has been designed and applied to the selective fluorescent turn-off detection of Hg2+ ions. The probe-Hg2+ system acted as a turn-on probe toward biothiols, including cysteine, homocysteine, and glutathione. The limits of detection of the probe toward Hg2+, cysteine, homocysteine, and glutathione are 0.52 μM, 0.74 μM, 0.31 μM, and 0.27 μM, respectively. The mechanisms are carefully confirmed by fluorescence spectrometry, UV-visible spectrometry, electrospray ionization mass spectra, hydrogen nuclear magnetic resonance, time-resolved fluorescence spectrum, and density functional theory calculation. Moreover, due to the presence of a morpholine group, the probe was successfully used to monitor Hg2+ and biothiols in the lysosomes of HeLa cells.