More efficient NIR photothermal therapeutic effect from intracellular heating modality than extracellular heating modality: an in vitro study

In this study, efforts were placed in giving some in vitro key clues to the question on which is more efficient for the cancer hyperthermia between intracellular and extracellular modalities. Near infrared (NIR) photothermal responsive gold nanorods (GNRs) were adopted to cause cellular thermolysis either from inside or outside of cells. GNRs were synthesized with the size of 30.4 nm (in length) x 8.4 nm (in width). Demonstrated by ICP-MS (inductively coupled plasmon mass spectroscopy), UV-Vis spectroscopy and transmission electron microscopy analyses, various cell uptake doses of nanoparticles were differentiated due to different molecular designs on GNRs surfaces and different types of cells chosen (three cancer cell lines and three normal ones). Under our continuous wavelengths (CW) NIR irradiation, it resulted that the cells which internalized GNRs died faster than the cells surrounded by GNRs. Furthermore, fluorescent images and flow cytometry data also showed that the NIR photothermal therapeutic effect was greater when the amount of internalized GNRs per cell was larger. Generally speaking, the GNRs assisted intracellular hyperthermia exhibited more precise and efficient control on the selective cancer ablation. To a larger degree, such a relationship between GNRs distribution and hyperthermia efficiency might be applied to wider spectra of cell types and heat-producing nanoparticles, which provided a promise for future cancer thermal therapeutic designs.