A non-solvatochromic fluorescent probe for imaging of lipid droplets in live cells and tissues

Lipid droplets (LDs) have recently attracted considerable attention owing to their crucial roles in both biological processes and disease pathogenesis. Visualization of LDs is fundamental for elucidating their roles in biological mechanisms and facilitating the early detection of diseases. Donor-acceptor (D-A) typed fluorescent probes have been extensively designed and utilized for the detection of LDs. However, such probes often exhibit a pronounced solvatochromic effect, leading to several limitations in detecting LDs, such as short excitation/emission wavelength, low specificity. Herein, we reported a non-solvatochromic D-A typed fluorescent probe S7 for LDs imaging in live cells and in vivo. S7 is polarity-dependent, which exhibits a very weak fluorescence in high-polar solvents owing to the photoinduced electron transfer (PET) mechanism but intense fluorescence in low-polarity environments without undergoing a solvatochromic blue shift. Except polarity, the fluorescent signal of S7 remains unaffected by factors such as viscosity, pH, ions, reactive oxygen species, reactive sulfur species, nucleic acids, proteins, and other biological molecules, allowing it to selectively light up LDs in live cells. Furthermore, this probe S7 exhibits an enhanced fluorescence intensity in tumor tissue when compared to normal tissue. This characteristic potentially provides an efficient and straightforward approach for tumor diagnosis.