A lipid droplet-targeted viscosity-sensitive fluorescent probe for visualization of tumor and NAFLD imaging

Non-alcoholic fatty liver disease (NAFLD) and tumors remain major clinical challenges, characterized by aberrant lipid droplets (LDs) accumulation and elevated microenvironmental viscosity as key pathological features. In this study, we developed a series of carbazole-based fluorescent probes, LJL1-LJL6. Through systematic screening of their photophysical properties and bioimaging performance, LJL1 was identified as the optimal candidate due to its superior viscosity sensitivity and LDs-targeting specificity. Specifically, LJL1, featuring a carbazole-thiophene electron-donating unit and a pyridine-based electron acceptor, exhibited an approximately 29-fold fluorescence enhancement in pure glycerol compared to water, with a robust linear correlation between fluorescence intensity and viscosity. Moreover, probe LJL1 demonstrated excellent photostability, low cytotoxicity, and exceptional LDs-targeting specificity. In biological applications, leveraging its wash-free imaging advantage, LJL1 successfully enabled real-time monitoring of dynamic LDs viscosity fluctuations under various physiological and pathological conditions, including oleic acid (OA) stimulation, starvation, pharmacological interventions, inflammatory responses, and ferroptosis. Furthermore, probe LJL1 exhibited outstanding spatiotemporal dynamic tracking capability for the lipophagy process. Mouse imaging studies revealed that LJL1 not only allowed imaging of 4 T1 tumor models but also sensitively monitored increased viscosity in liver tissues of NAFLD models, significantly distinguishing diseased livers from healthy ones. Collectively, this study establishes LJL1 as a high-performance LDs-targeted viscosity probe with substantial potential for mechanistic research of metabolic diseases.