LED-Activated NIR-II Gold Nanorods for Photothermal Therapy of 3D Melanoma Spheroids

Thermoplasmonics, an emerging field focused on heat generation via localized surface plasmon resonance (LSPR) in metallic nanostructures, presents significant potential for light-to-heat conversion in biomedical contexts. In this study, we report a distinct class of gold nanorods (GNRs) with longitudinal LSPRs spanning from 985 to 1282 nm, precisely tuned within the second near-infrared (NIR-II) biological window, as excellent photothermal candidates. To evaluate their intrinsic performance, colloidal suspensions of these GNRs were irradiated with low-power, low-cost LED sources emitting across a wide spectral range (505–1100 nm), both in and out of resonance with their plasmonic bands. Real-time thermal imaging was used to monitor heating and cooling dynamics, and photothermal conversion efficiency (η) was analytically determined, reaching values as high as 72%. Transmission electron microscopy (TEM) and UV–vis-NIR spectroscopy confirmed the high morphological uniformity and optical tunability of the nanorods, while finite-difference time-domain (FDTD) simulations provided further evidence for their absorption-driven behavior. Furthermore, in vitro experiments on B16.F10 melanoma cells, grown as monolayers (2D culture) or as spheroids (3D culture), demonstrated a dose-dependent toxicity of GNR 1060 over a wide range of studied concentrations. However, PEGylation of the GNR 1060 improved biocompatibility toward the B16.F10 melanoma cells in both monolayers and spheroids. When irradiated with an 1100 nm LED, both free and PEGylated GNR 1060 showed a promising photothermal effect, reducing the viability of melanoma spheroids by up to 40%. The photothermal effect of irradiated GNR 1060 in spheroids was also confirmed by 3D rescan confocal fluorescence imaging, which revealed cytotoxicity consistent with viability assay results. These findings demonstrate the robust thermoplasmonic capabilities of NIR-II GNRs and their potential as efficient, LED-activated nanoheaters for noninvasive cancer therapy.