Multiphoton imaging of melanoma 3D models with plasmonic nanocapsules

We report the synthesis of plasmonic nanocapsules and the cellular responses they induce in 3D
melanoma models for their perspective use as a photothermal therapeutic agent. The wall of the nanocap-
sules is composed of polyelectrolytes. The inner part is functionalized with discrete gold nanoislands. The
cavity of the nanocapsules contains a fluorescent payload to show their ability for loading a cargo. The
nanocapsules exhibit simultaneous two-photon luminescent, fluorescent properties and X-ray contrasting
ability. The average fluorescence lifetime (τ ) of the nanocapsules measured with FLIM (0.3 ns) is main-
tained regardless of the intracellular environment, thus proving their abilities for bioimaging of models
such as 3D spheroids with a complex architecture. Their multimodal imaging properties are exploited
for the first time to study tumorspheres cellular responses exposed to the nanocapsules. Specifically, we
studied cellular uptake, toxicity, intracellular fate, generation of reactive oxygen species, and effect on
the levels of hypoxia by using multi-photon and confocal laser scanning microscopy. Because of the high
X-ray attenuation and atomic number of the gold nanostructure, we imaged the nanocapsule-cell inter-
actions without processing the sample. We confirmed maintenance of the nanocapsules’ geometry in the
intracellular milieu with no impairment of the cellular ultrastructure. Furthermore, we observed the lack
of cellular toxicity and no alteration in oxygen or reactive oxygen species levels. These results in 3D
melanoma models contribute to the development of these nanocapsules for their exploitation in future
applications as agents for imaging-guided photothermal therapy