Polarity probes targeting different organelles based on aza-coumarin for monitoring ferroptosis and cellular senescence

Polarity within the cellular microenvironment is a key physical parameter that regulates multiple biological processes, and its dysregulation is closely associated with various diseases. This work designed and synthesized three polarity-sensitive fluorescent probes (3a-3c) based on an aza-coumarin fluorophore with a D-π-A structure, leveraging the intramolecular charge transfer (ICT) mechanism. The optical properties of the probes exhibited distinct solvatochromism in different solvents, with large Stokes shifts (3143, 2899, 3202 cm⁻¹ for 3a-3c, respectively), demonstrating excellent polarity responsiveness and biocompatibility. Colocalization experiments confirmed that, probes 3a-3c at a low concentration of 50 nM localized specifically to lysosomes, lipid droplets (LDs), and the endoplasmic reticulum (ER) with high Pearson's colocalization coefficients of 0.93, 0.98, and 0.97, respectively. In ferroptosis experiments, a marked reduction in fluorescence intensity (3.3-4.1-fold decrease) was observed for probes 3a-3c, highlighting the real-time monitoring capability of the probes. In addition, the probes also successfully distinguished polarity differences between normal and senescent cells in the cellular senescence experiment. This study thus provided a powerful tool and novel insights for elucidating the role of cellular polarity in pathophysiological processes such as ferroptosis and cellular senescence.