Quinoxalineimide-Based Semiconducting Polymer Nanoparticles as an Effective Phototheranostic for the Second Near-Infrared Fluorescence Imaging and Photothermal Therapy

Multifunctionaltheranostics play a critical role in improvingthe efficacy of photothermal therapy and tumor fluorescence imaging;however, they require the integration of complex components into asingle theranostic system, and their response in the second near-infrared(NIR-II) region is constrained by wavelengths of a photosensitizer.To address this issue, we herein developed a novel multifunctionalthiazole-fused quinoxalineimide semiconducting polymer (named PQIA-BDTT),which exhibits NIR-II fluorescence and photothermal properties. PQIA-BDTTnanoparticles achieved an impressively high photothermal conversionefficiency (72.6%) in laser (1064 nm)-induced photothermal therapyat a safe maximum permissible exposure, demonstrating their capabilityas an effective photothermal agent. Moreover, PQIA-BDTT nanoparticlescan be used as a reference for NIR-II fluorescence imaging under alow laser fluence. The tumor size and location in 4T1 mice intravenouslyinjected with the PQIA-BDTT nanoparticles could be preciselyidentified through NIR-II fluorescence imaging, which also exhibitedremarkable photothermal antitumor efficacy by in vitro and in vivo therapy.Overall, this study demonstrates that introducing a thiazole-fusedquinoxalineimide acceptor unit into a donor-acceptor conjugatedpolymer is an effective strategy for the synthesis of novel multifunctionaltheranostic systems, which provides a novel platform for designingtheranostic agents for biomedical applications.

Automated summary

In this study, a novel multifunctional thiazole-fused quinoxalineimide semiconducting polymer (PQIA-BDTT) was developed, which exhibits NIR-II fluorescence and photothermal properties for photothermal therapy and tumor fluorescence imaging. The nanoparticles of PQIA-BDTT achieved high photothermal conversion efficiency and can be used for NIR-II fluorescence imaging at low laser fluence.