Herceptin-conjugated plasmonic gold nanocapsules for targeted NIR-II photothermal therapy†

In recent years, researchers have extensively studied nanomaterials for plasmonic photothermal therapy (PPTT), with most of the research focused on those active in the near-infrared I (NIR I) window (λ = 650–950 nm). However, there is growing interest in developing nanomaterials that are active in the near-infrared II (NIR II) region (λ = 950–1300 nm) due to the better penetrability and higher tolerance limit of NIR II light by human skin. In this study, the potential of gold nanocapsules (Au Ncap) with a rattle-like structure, consisting of a solid gold bead core and a porous, thin, rod-shaped gold shell was investigated for PPTT. Specifically, the targeted in vitro photothermal activity of Herceptin-conjugated gold nanocapsules that are active in both the NIR I and II regions are explored towards the Her2 positive SK-BR-3 breast cancer cell line. The conjugation of SH-PEG and Herceptin molecules on the surface of gold nanocapsules was validated through a detailed X-ray photoemission spectroscopy (XPS) analysis. The Au Ncap exhibited high photothermal conversion efficiency of 38.6% and in vitro PPTT results showed its excellent cytotoxicity against the SK-BR-3 cell line leading to apoptotic cell death. These findings suggest that this nanostructure can serve as an efficient photothermal agent in the NIR II region showing excellent PPTT activity at a low laser power density of 0.5 W cm⁻².