Two-photon fluorescence probes for mitochondria imaging and detection of sulfite/bisulfite in living cells

Sulfur dioxide derivatives, i.e., sulfite (SO32−) and bisulfite (HSO3−) play important roles in numerous physiologically essential processes of living systems. SO32− and HSO3− with abnormal levels have close relation with many diseases including acute symptoms of respiratory disease, cardiovascular disease, cancer and neurological disorder. Herein, we presented two new two-photon fluorescence probes based on diethylaminecoumarin skeleton with pyridinum (1-[2-(7-Diethylamino-2-oxo-2H-chromen-3-yl)-2-oxo-ethyl]-pyridinium; bromide, C-Py) and imidazole (1-[2-(7-diethylamino-2-oxo-2H-chromen-3-yl)-2-oxo-ethyl]-3-methyl-3H-imidazol-1-ium; bromide, C-Im) as terminal group. The probes showed highly sensitive and selective response to sulfite/bisulfite on the basis of intermolecular hydrogen bonding action between methylene and sulfite/bisulfite. The probes have excellent cell permeability, and a series of uptake inhibition experiments suggested that the probes possibly enter cells through an energy-dependent pathway and endocytosis is impossible to be responsible for cell-membrane penetration process. The probes could specifically target mitochondria by two-photon imaging in living cells, and exhibit nearly no mitochondrial membrane potential damage. Moreover, the probes could be successfully applied for two-photon imaging of mitochondial SO32− and HSO3− in living cells. Negligible cytotoxicity, high mitochondrion selectivity, good recognition properties to sulfite/bisulfite, good cellular uptake and cell membrane penetration will allow them to find valuable application in biomedical research field for sulfite/bisulfite detection.