Semiconducting polymer-based nanoparticles with strong absorbance in NIR-II window for in vivo photothermal therapy and photoacoustic imaging.

Near-infrared (NIR) light-induced photothermal therapy (PTT) has attracted much interest in recent years. In the NIR region, tissue penetration ability of the second biological near-infrared window (1000-1350 nm) is recognized to be stronger than that of the first window (650-950 nm). However, NIR light absorbers in the second NIR region (NIR-II) have been scant even though various NIR light absorbers in the first NIR region (NIR-I) have been widely explored. In this work, a thieno-isoindigo derivative-based semiconducting polymer, PBTPBF-BT, were formulated into PEGylated nanoparticles. The obtained nanoparticle NP exhibited strong absorption in NIR-II region, inherent high photothermal conversion efficacy, and excellent photostability. The in vitro and in vivo PTT study employing 1064 nm laser in NIR-II window revealed that NP could efficiently ablate tumor cell at a power density of 0.42 W/cm (the skin tolerance threshold value). Moreover, NP with excellent photostability exhibited enhanced photoacoustic (PA) imaging of tumor in living mice, suggesting the great probability of using NP for in vivo PA imaging-guided PTT in the NIR-II window.