Protein-encapsulated long-wavelength fluorescent probe hybrid for imaging lipid droplets in living cells and mice with non-alcoholic fatty liver

Non-alcoholic fatty liver disease (NAFLD) is prevalent worldwide as a chronic liver disease that not only gives rise to hepatic complications, but leads to other chronic diseases such as type 2 diabetes and atherosclerosis. The aberrant accumulation of lipid droplets (LDs) in hepatocytes is a prominent signature of NAFLD. However, conventional techniques lack the capability to effectively monitor the dynamic changes in LD levels during NAFLD with living organisms. Hence, it is imperative to develop LD-specific long-wavelength fluorescent probes with high imaging contrast for the in-situ diagnosis of NAFLD. In this study, we synthesized a new LD-selective long-wavelength fluorescent probe, denoted as LD-1, based on the twisted intramolecular charge transfer (TICT) mechanism. The probe exhibits a large Stokes shift and intensive fluorescence emission in nonpolar and viscous solutions. By self-assembling LD-1 with bovine serum albumin (BSA), a biocompatible, long-wavelength fluorescent probe hybrid, LD-1@BSA, was formed, allowing for LDs to be selectively imaged in hepatocytes. Moreover, LD-1@BSA successfully discriminates NAFLD cells before and after drug treatment, and achieves non-invasive and real-time monitoring of LD accumulation in a mouse model of NAFLD.