Palladium Nanocapsules for Photothermal Therapy in the Near-Infrared II Biological Window

Recent developments in nanomaterials with programmableopticalresponses and their capacity to modulate the photothermal effect inducedby an extrinsic source of light have elevated plasmonic photothermaltherapy (PPTT) to the status of a favored treatment for a varietyof malignancies. However, the low penetration depth of near-infrared-I(NIR-I) lights and the need to expose the human body to a high laserpower density in PPTT have restricted its clinical translation forcancer therapy. Most nanostructures reported to date exhibit limitedperformance due to (i) activity only in the NIR-I region, (ii) theuse of intense laser, (iii) need of large concentration of nanomaterials,or (iv) prolonged exposure times to achieve the optimal hyperthermiastate for cancer phototherapy. To overcome these shortcomings in plasmonicnanomaterials, we report a bimetallic palladium nanocapsule (Pd Ncap)witha solid gold bead as its core and a thin, perforated palladium shell withextinction both in the NIR-I as well as the NIR-II region for PPTTapplications toward cancer therapy. The Pd Ncap demonstrated exceptionalphotothermal stability with a photothermal conversion efficiency of & SIM;49% at the NIR-II (1064 nm) wavelength region at a very lowlaserpower density of 0.5 W/cm(2). The nanocapsules were furthersurface-functionalized with Herceptin (Pd Ncap-Her) to target thebreast cancer cell line SK-BR-3 and exploited for in vitro PPTT applications using NIR-II light. Pd Ncap-Her caused more than98% cell death at a concentration of just 50 & mu;g/mL and a laserpower density of 0.5 W/cm(2) with an output power of only100 mW. Flow cytometric and microscopic analyses revealed that PdNcap-Her-induced apoptosis in the treated cancer cells during PPTT.Additionally, Pd Ncaps were found to have reactive oxygen species(ROS) scavenging ability, which can potentially reduce the damageto cells or tissues from ROS produced during PPTT. Also, Pd Ncap demonstratedexcellent in vivo biocompatibility and was highlyefficient in photothermally ablating tumors in mice. With a high photothermalconversion and killing efficiency at very low nanoparticle concentrationsand laser power densities, the current nanostructure can operate asan effective phototherapeutic agent for the treatment of differentcancers with ROS-protecting ability.

Automated summary

Recent developments in nanomaterials have led to the application of plasmonic photothermal therapy (PPTT) for the treatment of cancer. However, the limitations of low penetration depth of NIR-I lights and high laser power density have restricted its clinical translation. To overcome these shortcomings, the researchers have developed a bimetallic palladium nanocapsule (Pd Ncap) that can be used for PPTT in both NIR-I and NIR-II regions. The Pd Ncap exhibits excellent photothermal stability and killing efficiency, with the potential to protect cells from reactive oxygen species (ROS) produced during PPTT.