Polycyclic naphthalenediimide-based nanoparticles for NIR-II fluorescence imaging guided phototherapy

Optical imaging and phototherapy in the second near-infrared window (NIR-II, 900–1700 nm) can reduce tissue auto-fluorescence and photon scattering, which facilitates higher spatial resolution and deeper tissue penetration depth for solid tumor theranostics. Herein, a polycyclic naphthalenediimide (NDI) based chromophore 13-amino-4,5-dibromo-2,7- di(dodecan-6-yl)-1H-isoquinolino[4,5,6-fgh]naphtho[1,8-bc][1,9]phenanthroline-1,3,6,8(2H,7H,9H)-tetraone (NDI-NA) was designed and synthesized. With large polycyclic π-systems, NDI-NA molecule possesses broad near-infrared (NIR) absorption (maximum at 777 nm) and emission (maximum at 921 nm). By nanoprecipitation, NDI-NA nanoparticles (NPs) were formed in aqueous solution with J-aggregative state, which showed huge red-shift in both absorption spectrum (maximum at 904 nm) and emission spectrum (maximum at 1,020 nm), endowing NDI-NA NPs efficient NIR-II fluorescence imaging capability. Besides, the NPs present effective tumor-targeting capability in vivo based on the enhanced permeation and retention (EPR) effect. More importantly, NDI-NA NPs simultaneously have high photothermal conversion efficiency (30.8%) and efficient reactive oxygen species generation ability, making them remarkably phototoxic to cancer cells. The polycyclic chromophore based multifunctional NDI-NA NPs as NIR-II phototheranostic agents possess bright future for clinical NIR-II imaging-guided cancer phototherapy.