A multifunctional fluorescent probe for dual-color visualization of intracellular mitochondria and lipid droplets and monitoring of SO2 in vivo

Mitochondria and lipid droplets (LDs) are organelles involved in intracellular lipid and energy metabolism, and their complicated interplays are critical for maintaining cellular homeostasis. However, the fluorescent probes capable of simultaneously and discriminatively visualizing mitochondria and LDs are severely insufficient, which greatly limits the investigation of the interaction between two organelles in cells. In addition, abnormal SO2 levels can have harmful effects on living organisms. Monitoring the changes of SO2 levels in vivo is of great significance for biological and medical research. In this work, a SO2-dependent strategy was proposed for the first time to construct the new functional fluorescence conversion probe MLD-SO2 for two-color visualization of mitochondria and LDs. Under normal physiological conditions, the cationic form enabled the probe to selectively target the mitochondria and emit red fluorescence. In addition, based on SO2-driven nucleophilic addition reaction, the probe MLD-SO2 was converted to the neutral lipophilic structure in the presence of SO2, which targeted to LDs and displayed a strong blue emission. Importantly, mitochondria and LDs could be visualized simultaneously in the red and blue emission channels under the appropriate amount of SO2 exposure. Furthermore, the probe MLD-SO2 has been successfully employed to monitor the SO2 changes in zebrafish and mung bean sprouts. The remarkable imaging performances render the novel probe MLD-SO2 as a powerful tool for deciphering the interactions between mitochondrial and LDs and monitoring SO2 in different organisms.