Red-emissive carbon quantum dots minimize phototoxicity for rapid and long-term lipid droplet monitoring

Long-term fluorescence monitoring of subcellular organelles is crucial for cellular physiology and pathology studies. Lipid droplets (LDs) are increasingly recognized for their involvement in various biological processes, to influence disease development through diverse behaviors However, existing LD probes face challenges in achieving high targeting and long-term monitoring due to poor photostability and long-term phototoxicity. Carbon quantum dots (CQDs) have gained prominence due to their exceptional fluorescence properties, but their prevalent blue excitation wavelength presents difficulties for long-term imaging. Herein, we synthesized red-emissive carbon quantum dot (R-CQDs) with superior photobleaching resistance and red-emission, thus enabling harmlessly fluorescence monitoring of cells longer than 3 h. In addition, R-CQD exhibits suitable amphiphilicity and remarkable solvatochromic effect, allowing rapid targeting to LDs for immediate imaging without cumbersome washing steps. Hence, R-CQD shows high performance for extended observation of dynamic LD behavior in various biological processes, which is confirmed by documenting the course of LDs during starvation as well as lipotoxicity. Compared to commercial probes, R-CQD extends live cell imaging time by at least 9-fold, facilitating the study of LD behavioral characteristics under diverse physiological or pathological conditions. This work provides a reliable fluorescence tool for tracking intercellular microenvironment dynamically thus to understand the divers biological or disease mechanism.