Aggregation-Enhanced Photophysical Performance of D-π-A Structured Hemicyanine for NIR-II Fluorescent and Photoacoustic Imaging-Guided Photothermal Therapy

Near-infrared (NIR)-II fluorescence and photoacoustic (PA) dual-model imaging-guided photothermal therapy (PTT) can precisely diagnose and treat tumors and evaluate the therapeutic efficacy in real-time. Herein, we utilized a donor-π-acceptor (D-π-A) structured hemicyanine dye (named M1) with a large conjugated structure and strong intramolecular charge transfer effect and demonstrated that the aggregation of M1 could significantly enhance its photophysical performance by improving its photostability and photothermal conversion capability as compared with M1 in a single molecular state. Furthermore, we prepared water-dispersible NIR-II fluorescent nanoparticles (M1 NPs) by wrapping M1 with DSPE-PEG2000-NH2. The obtained M1 NPs exhibit strong NIR-I absorption and NIR-II fluorescence with their maxima at 734 and 1040 nm, respectively, with a fluorescence quantum yield of 2.84%. Moreover, M1 NPs also exhibit excellent biocompatibility, good photostability, and high photothermal conversion efficiency of 77.5%. In vitro and in vivo experiments reveal that M1 NPs can effectively image tumors through NIR-II fluorescence and PA signals, inhibit DNA replication, trigger cytoskeleton collapse, and eventually induce tumor cell apoptosis under 808 nm laser irradiation. Based on these outstanding properties, the application of M1 NPs in PA and NIR-II fluorescence imaging-guided PTT of tumors is demonstrated.