Dual-Peak Absorbing Semiconducting Copolymer Nanoparticles for First and Second Near-Infrared Window Photothermal Therapy: A Comparative Study

Abstract

Near-infrared (NIR) light is widely used for noninvasive optical diagnosis and phototherapy. However, current research focuses on the first NIR window (NIR-I, 650–950 nm), while the second NIR window (NIR-II, 1000–1700 nm) is far less exploited. The development of the first organic photothermal nanoagent (SPN_I-II) with dual-peak absorption in both NIR windows and its utilization in photothermal therapy (PTT) are reported herein. Such a nanoagent comprises a semiconducting copolymer with two distinct segments that respectively and identically absorb NIR light at 808 and 1064 nm. With the photothermal conversion efficiency of 43.4% at 1064 nm generally higher than other inorganic nanomaterials, SPN_I-II enables superior deep-tissue heating at 1064 nm over that at 808 nm at their respective safety limits. Model deep-tissue cancer PTT at a tissue depth of 5 mm validates the enhanced antitumor effect of SPN_I-II when shifting laser irradiation from the NIR-I to the NIR-II window. The good biodistribution and facile synthesis of SPN_I-II also allow it to be doped with an NIR dye for fluorescence-imaging-guided NIR-II PTT through systemic administration. Thus, this study paves the way for the development of new polymeric nanomaterials to advance phototherapy.

The first dual-peak absorbing organic nanoagent with nearly identical absorbance at 808 and 1064 nm is developed from a semiconducting copolymer. Such a nanoagent not only enables deep-tissue photothermal cancer therapy in both the first and second near-infrared windows, but also permits a fair comparative study to reveal the advantage of shifting the laser light into a longer wavelength region for phototherapy.

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