Au Nanorod Design as Light-Absorber in the First and Second Biological Near-Infrared Windows for <i>in Vivo</i> Photothermal Therapy

TLDR

Photothermal cancer therapy with NIR laser radiation is emerging, exploiting two biological transparency windows (650‑950 nm and 1000‑1350 nm) that allow deep tissue penetration, yet sub‑100‑nm absorbers in the second window are scarce. The study reports designing a sub‑100‑nm Au nanorod with a rod‑in‑shell structure responsive to both NIR windows for hyperthermia therapy. The authors engineered a sub‑100‑nm Au nanorod with a rod‑in‑shell design, tuning its UV‑vis‑NIR spectrum by adjusting the core‑shell gap to shift absorption into the 650‑950 nm and 1000‑1350 nm windows for hyperthermia therapy. In vitro, the rod‑in‑shell nanorods produced extensive cell damage beyond the laser spot, and in vivo they achieved superior solid‑tumor ablation with 808 nm or 1064 nm diode lasers, outperforming conventional Au nanorods.

Abstract

Photothermal cancer therapy using near-infrared (NIR) laser radiation is an emerging treatment. In the NIR region, two biological transparency windows are located in 650-950 nm (first NIR window) and 1000-1350 nm (second NIR window) with optimal tissue transmission obtained from low scattering and energy absorption, thus providing maximum radiation penetration through tissue and minimizing autofluorescence. To date, intensive effort has resulted in the generation of various methods that can be used to shift the absorbance of nanomaterials to the 650-950 nm NIR regions for studying photoinduced therapy. However, NIR light absorbers smaller than 100 nm in the second NIR region have been scant. We report that a Au nanorod (NR) can be designed with a rod-in-shell (rattle-like) structure smaller than 100 nm that is tailored to be responsive to the first and second NIR windows, in which we can perform hyperthermia-based therapy. In vitro performance clearly displays high efficacy in the NIR photothermal destruction of cancer cells, showing large cell-damaged area beyond the laser-irradiated area. This marked phenomenon has made the rod-in-shell structure a promising hyperthermia agent for the in vivo photothermal ablation of solid tumors when activated using a continuous-wave 808 m (first NIR window) or a 1064 nm (second NIR window) diode laser. We tailored the UV-vis-NIR spectrum of the rod-in-shell structure by changing the gap distance between the Au NR core and the AuAg nanoshell, to evaluate the therapeutic effect of using a 1064 nm diode laser. Regarding the first NIR window with the use of an 808 nm diode laser, rod-in-shell particles exhibit a more effective anticancer efficacy in the laser ablation of solid tumors compared to Au NRs.