Polymer Dots for Precision Photothermal Therapy of Brain Tumors in the Second Near-Infrared Window: A Mini-Review

Tremendous endeavors have been made to improve the sensitivity of brain tumor detection and the efficacy of treatment in the past decades. However, the cure rate of brain tumor patients is not significantly increased due to the limited therapeutic window for breaking the blood-brain barrier (BBB). To pave new avenues for precision brain tumor treatment, a couple of strategies have been proposed and carried out for enhanced cancer theranostics. In particular, photothermal therapy (PTT) in the second nearinfrared (NIR-II) window (1000-1700 nm) has exhibited its unique advantages in precise and spatiotemporal destruction and removal of tumor tissues. Compared with the first near-infrared (NIR-I), NIR-II with longer wavelengths allows for reduced light-tissue interaction, resulting in increased permissible power density and enhanced photon penetration for deep-tissue theranostics applications. Meanwhile, conjugated polymer dots (Pdots) show that it can cross the BBB, which can serve as a molecular imaging probe and concurrently as photothermal agent for brain tumor due to its good biocompatibility and robust photophysical properties. This mini-review first introduces the therapeutic mechanisms of PTT, and then the recent advances in design and functionalization strategies of NIR-II Pdots as well as the applications of these nanoagents in brain tumor diagnosis, treatment, and theranostics are briefly reviewed. Further, the main challenges and promising perspectives of these photothermal Pdots in terms of clinical translation are also addressed.