Construction of Novel Pyrrole-Derivative-Based Fluorescent Platforms and Development of Polarity-Sensitive Probes for Imaging Lipid Droplets in Cells and Zebrafish

Lipid droplets (LDs), serving as central hubs in lipid metabolism, exhibit dynamic changes closely associated with diseases such as obesity, diabetes, and cancer. Visualizing LDs is crucial for elucidating their role in biological mechanisms and facilitating early disease detection. Donor-acceptor (D-A) type fluorescent probes have been widely designed and employed for LD detection. In this study, we designed and constructed a pyrrole-based molecular scaffold with a symmetrical architecture. Through modulation of para-substituents, a series of novel fluorescent dyes ( 3a-e ) were successfully synthesized. Experimental characterization revealed that the dimethylamino-modified dye 3e , characterized by a typical D-A-D structure, exhibits red emission (λ _em  ≈ 608 nm in THF), significant solvatochromism, and a large Stokes shift (134 nm). To enhance its stability, the pyrrole N-H group of 3e was further methylated, successfully yielding a fluorescent LD probe, Py-LD . Py-LD not only exhibits a large Stokes shift (142 nm in THF), significantly reducing self-absorption and enhancing imaging signal-to-noise ratio, but also demonstrates excellent polarity sensitivity, enabling polarity detection. Furthermore, Py-LD displays high specificity and stability. It was successfully applied for dynamic tracking of LDs in live cells and lipid imaging within the zebrafish yolk sac, providing a novel tool for LD monitoring.