Easy access to 2,1,3-benzothiadiazole-based symmetric deep red-AIEgens for concurrent staining of lipid droplets and lysosomes

Abstract

Deep-red-emissive aggregation-induced emission-active luminogens (AIEgens) have emerged as powerful tools for advanced noninvasive cancer diagnosis, selective imaging, and therapeutic applications due to their deep tissue penetration, high contrast, high photostability, and excellent biocompatibility. Unlike traditional fluorophores that undergo aggregation-caused quenching (ACQ), AIEgens become brightly emissive upon aggregation, enabling real-time visualization in complex biological environments. A major challenge in cellular imaging is the simultaneous and highly specific labeling of lipid droplets (LDs) and lysosomes, two organelles closely interconnected through lipophagic processes (degradation of LDs by lysosomes) and central to metabolic regulation. Existing small-molecule dyes often lack dual-targeting capability and typically diffuse throughout the cytoplasm before localizing to their intended targets. Herein, we provide easy access to three newly designed 2,1,3-benzothiadiazole (BTD)-based D–π–A–π–D symmetric luminogens, MBM, DBD, and TBT, engineered for staining LDs and lysosomes. Even autophagosomes, a dynamic and double-membrane-bound organelle, are also stained with these probes. They exhibit strong red emission (630–740 nm) in both solid-state and highly aqueous media, demonstrating robust AIE properties. Colocalization studies confirm their reliable targeting of both organelles, supported by favourable binding affinities and other cross-experiments. The overall balance of hydrophobicity and hydrophilicity of the photostable probes MBM, DBD, and TBT exhibited organelle specificity, photostability, efficient uptake, and tunable cytotoxicity. Thus, these red-emitting probes are recognized as promising candidates for multifunctional bioimaging and therapeutic applications. The high stability, low photobleaching, and large Stokes shifts make these dyes superior to commercially available conventional dyes like Nile Red.