Substituent Effects in BODIPY in Live Cell Imaging.

Small-molecule organoselenium-based fluorescent probes possess great capacity in understanding biological processes through the detection of various analytes such as reactive oxygen/nitrogen species (ROS/RNS), biothiols (cysteine, homocysteine and glutathione), lipid droplets, etc. Herein, we present how substituents on the BODIPY system play a significant part in the detection of biologically important analytes for in vitro conditions and live cell imaging studies. The fluorescence of the probe was quenched by 2-chloro and 6-phenyl selenium groups; the probe shows high selectivity with NaOCl among other ROS/RNS, and gives a turn-on response. The maximum fluorescence intensity is attained within ≈1-2 min with a low detection limit (19.6 nm), and shows a ≈110-fold fluorescence enhancement compared to signals generated for other ROS/RNS. Surprisingly, in live cell experiments, the probe specifically located and accumulated in lipid droplets, and showed a fluorescence turn-on response. We believe this turn-on response occurred because of aggregation-induced emission (AIE), which surprisingly occurred only by introducing one lipophilic mesityl group at the meso position of the BODIPY.