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 NPPBTPBF-BT 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 NPPBTPBF-BT could efficiently ablate tumor cell at a power density of 0.42 W/cm2 (the skin tolerance threshold value). Moreover, NPPBTPBF-BT with excellent photostability exhibited enhanced photoacoustic (PA) imaging of tumor in living mice, suggesting the great probability of using NPPBTPBF-BT for in vivo PA imaging-guided PTT in the NIR-II window.