Simultaneous Visualization of Mitochondria and Lysosome by a Single Cyanine Dye: The Impact of the Donor Group (-NR2) Towards Organelle Selectivity.

A benzothiazolium-based hemicyanine dye (probe 3) has been synthesized by attaching a morpholine group into a phenyl benzothiazolium skeleton. Probe 3 exhibited interesting photophysical characteristics including red emission (λem ≈600 nm), enhanced Stokes shift (Δλ ≈80 nm) and sensitivity to solvent polarity. Although the probe 3 exhibited almost no emission in aqueous environments (φfl ≈0.002), its fluorescence could be increased by ≈50 fold in organic solvents (φfl ≈0.10), making it possible for live cell imaging under wash-free conditions. Probe 3 exhibited excellent ability to visualize cellular mitochondria and lysosomes simultaneously, as observed from fluorescence confocal microscopy. In addition, probe 3 also exhibited good biocompatibility (calculated LC50 > 20 µM) and high photostability.