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.