Stimulated Emission Depletion (STED) Super-Resolution Imaging with an Advanced Organic Fluorescent Probe: Visualizing the Cellular Lipid Droplets at the Unprecedented Nanoscale Resolution

Lipid droplets (LDs) are important cellular organelles associated with many physiological processes. To visualize and study LDs, particularly the nascent LDs (diameters of 30–60 nm), super-resolution fluorescence imaging techniques with nanoscale resolution are regarded as the most appealing tools. However, this idea is largely limited by the availability of advanced LDs fluorescent probes that are capable of the proper super-resolution imaging techniques. Therefore, visualizations of LDs at the nanoscale resolution are very challenging and highly attractive. Herein, a distyrylbenzene-based molecule Lipi-DSB is sophisticatedly developed as a new LDs fluorescent probe that is capable of the stimulated emission depletion (STED) super-resolution imaging. The probe Lipi-DSB displays superior properties including high photostability and brightness, large Stokes shift, low saturation intensity for STED laser, and good staining specificity toward LDs. Employing this fluorescent probe for STED imaging provides the state-of-the-art super-resolution imaging of LDs in terms of (1) the highest resolution (58 nm) of LDs up to date; (2) the maximum frames (1000 frames, 21.8 min) of time-lapse live imaging of LDs; (3) the first visualization of the fusion process of nascent LDs; (4) and the highest quality of 3D imaging of LDs. Thus, the dynamics and spatial distribution of LDs are visualized at the unprecedented nanoscale resolution, highlighting the utility of this fluorescent probe in STED super-resolution imaging.