Real-time monitoring of newly acidified organelles during autophagy in living cells is highly desirable for a better understanding of intracellular degradative processes. Herein, we describe a reaction-based boron dipyrromethene (BODIPY) dye containing strongly electron-withdrawing diethyl 2-cyanoacrylate groups at the α-positions. The probe exhibits intense red fluorescence in acidic organelles or the acidified cytosol while exhibiting negligible fluorescence in other regions of the cell. The underlying mechanism is a nucleophilic reaction at the central meso-carbon of the indacene core, resulting in the loss of π-conjugation entailed by dramatic spectroscopic changes of more than 200nm between its colorless, non-fluorescent leuco-BODIPY form and its red and brightly emitting form. The reversible transformation between red fluorescent BODIPY and leuco-BODIPY along with negligible cytotoxicity qualifies such dyes for rapid and direct intracellular lysosome imaging and cytosolic acidosis detection simultaneously without any washing step, enabling the real-time monitoring of newly acidified organelles during autophagy.
This work has been published in Communications Biology (DOI：https://doi.org/10.1038/s42003-019-0682-1) as a Featured article. Dr. Hanzhuang Liu and Ms. Wenting Song contributed equally，Prof. Zhen Shen from State Key Laboratory of Coordination Chemistry, School of Chemistry and Chemical Engineering, Nanjing University and Prof. Knut Rurack from Bundesanstalt für Materialforschung und -prüfung (BAM), Germany are corresponding authors. Financial support was provided by the National Natural Science Foundation of China (21771102).
Fig. 1 Schematic illustration of lighting up lysosomes and newly acidified organelles. a Potential mesomeric resonance structures of indacene skeleton. b Reversible transformation between BODIPY form in CH2Cl2 and leuco-BODIPY form in MeOH, and aspired signalling response during autophagy.