Donor–Acceptor–Donor Near-Infrared-II Aggregation-Induced Emission Luminogens (AIEgens) Encapsulated within Nanometer-Sized Exosomes for Tumor Imaging

Developing organic aggregation-induced emission luminogens (AIEgens) with a donor–acceptor–donor (D–A–D) structure improves fluorescence imaging for biological applications due to their deep tissue penetration, high fluorescence quantum yield, and good biocompatibility. However, compared to the systematically well-explored near-infrared-I (NIR-I, 650–900 nm) AIEgens, the research on organic D–A–D-type near-infrared-II (NIR-II, 1000–1700 nm) AIEgens received a snub, by contrast, owing to their lack of diversity, low AIE character, and poor tumor accumulation, which has become a bottleneck in the bioimaging field. Herein, we report a D–A–D-type organic NIR-II fluorophore with typical AIE character (α AIE > 4) through careful manipulation of the electron donor and acceptor. The tumor-associated macrophage (TAM)-derived exosomes with nanometer size were used as templates to encapsulate the NIR-II AIEgens ( o BBT-DPNA) in a well-defined structure (named as AIE@Exo). The AIE@Exo displayed a superb aggregation-intensified NIR-II fluorescence with a maximum emission peak at 1052 nm as well as a calculated fluorescence quantum yield (QY) of 3.1%. Moreover, the in vivo application of AIE@Exo in efficient NIR-II fluorescence imaging of whole-body vessels and tumor was successfully demonstrated in living mice. Overall, the nanometer-sized biomimetic nanoparticles represent successful NIR-II AIE nanoparticles for biomedical imaging.