A highly efficient fluorescent probe based on tetrahydroxanthylium-coumarin for the detection of bisulfite in mitochondria

The addition of bisulfite to an electron-withdrawing double bond has been reported for the design of a bisulfite probe; however, the selectivity of this reaction is usually influenced by an oxidation reaction with hypochlorite. Herein, a probe (probe 1) with tetrahydroxanthylium and coumarin units was designed for the detection of bisulfite. The probe 1 exhibited high selectivity, an obvious colour change from blue to yellow and a large turn-on signal (144-fold enhancement) with green emission towards bisulfite in an acetonitrile-phosphate buffered saline (1 : 9, v/v) solution. In addition, an excellent linear relationship between the fluorescence intensity at 514 nm and bisulfite concentration (0-2 equivalent) was obtained. Moreover, the response time of the probe 1 towards bisulfite was within the order of several seconds, and the detection limit was calculated to be 22.8 nM. The mechanism of the detection reaction was proved by both the H-1 NMR analysis and time-dependent density functional theory (TDDFT) calculations. The results of the fluorescence co-localization studies demonstrate that the probe 1 is a mitochondria-targeted fluorescent probe that can be used for the bioimaging of bisulfite in living HeLa cells.